Pioneer Bond Fund

Class A Shares (PIOBX)	Class B Shares (PBOBX)	Class C Shares (PCYBX)
Class K Shares (PBFKX)	Class R Shares (PBFRX)	Class Y Shares (PICYX)
Class Z Shares (PIBZX)

Summary ProspectusDecember 15, 2012

Before you invest, you may want to review the fund’s prospectus, which contains more information about the fund and its risks. You can find the fund’s prospectus, statement of additional information and other information about the fund online at http://us.pioneerinvestments.com/misc/prospectus.jsp. You also can obtain this information at no cost by calling 1-800-225-6292 or by sending an email request to askpioneer@pioneerinvestments.com. The fund’s current prospectus and statement of additional information, dated December 15, 2012, and the independent registered public accounting firm’s report and financial statements in the fund’s annual report to shareholders dated June 30, 2012, are incorporated by reference into this summary prospectus.

Investment objectives

To provide current income from an investment grade portfolio with due regard to preservation of capital and prudent investment risk. The fund also seeks a relatively stable level of dividends; however, the level of dividends will be maintained only if consistent with preserving the investment grade quality of the portfolio.

Fees and expenses of the fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the fund.

You may qualify for sales charge discounts if you or your family invest, or agree to invest in the future, at least $100,000 in Class A shares of the Pioneer funds. More information about these and other discounts is available from your investment professional and in the “Sales charges” section of the prospectus beginning on page 43 and the “Sales charges” section of the statement of additional information beginning on page 64.

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Summary Prospectus

Shareowner fees
(fees paid directly from your investment)	Class A	Class B	Class C	Class K	Class R	Class Y	Class Z
Maximum sales charge (load) when you buy shares (as a percentage of offering price)	4.50%	None	None	None	None	None	None
Maximum deferred sales charge (load) (as a percentage of offering price or the amount you receive when you sell shares, whichever is less)	None	4%	1%	None	None	None	None

Annual fund operating expenses
(expenses that you pay each year as a percentage of the value of your investment)	Class A	Class B	Class C	Class K	Class R	Class Y	Class Z
Management Fees	0.49%	0.49%	0.49%	0.49%	0.49%	0.49%	0.49%
Distribution and Service (12b-1) Fees	0.25%	1.00%	1.00%	0.00%	0.50%	0.00%	0.00%
Other Expenses1	0.29%	0.53%	0.24%	0.07%	0.36%	0.16%	0.34%
Total Annual Fund Operating Expenses2	1.03%	2.02%	1.73%	0.56%	1.35%	0.65%	0.83%
Less: Fee Waiver and Expense Reimbursement2	–0.18 %	–0.12%	0.00%	0.00%	-0.10%	0.00%	–0.18%
Net Expenses2	0.85%	1.90%	1.73%	0.56%	1.25%	0.65%	0.65%

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Other expenses for Class K shares are based on estimated amounts for the current fiscal year.

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The fund’s investment adviser has contractually agreed to limit ordinary operating expenses to the extent required to reduce fund expenses to 0.85%, 1.90%, 1.25% and 0.65% of the average daily net assets attributable to Class A, Class B, Class R and Class Z shares, respectively. These expense limitations are in effect through November 1, 2014. There can be no assurance that the adviser will extend the expense limitations beyond such times. While in effect, the arrangement may be terminated for a class only by agreement of the adviser and the Board of Trustees.

Example

This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the fund for the time periods shown and then, except as indicated, redeem all of your shares at the end of

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those periods. It also assumes that (a) your investment has a 5% return each year and (b) the fund's total annual operating expenses remain the same except for year one (which considers the effect of the expense limitation). Although your actual costs may be higher or lower, based on these assumptions your costs would be:

	If you redeem your shares				If you do not redeem your shares
	Number of years you own your shares
	1	3	5	10	1	3	5	10
Class A	$533	$746	$976	$1,637	$533	$746	$976	$1,637
Class B	593	922	1,177	2,083	193	622	1,077	2,083
Class C	276	545	939	2,041	176	545	939	2,041
Class K	57	179	313	701	57	179	313	701
Class R	127	418	730	1,615	127	418	730	1,615
Class Y	66	208	362	810	66	208	362	810
Class Z	66	247	443	1,009	66	247	443	1,009

Portfolio turnover

The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the fund's performance. During the most recent fiscal year, the fund's portfolio turnover rate was 21% of the average value of its portfolio.

Principal investment strategies

Normally, the fund invests at least 80% of its net assets (plus the amount of borrowings, if any, for investment purposes) in debt securities issued or guaranteed by the U.S. government, its agencies and instrumentalities, investment grade debt securities (including convertible debt) of corporate or other issuers and cash, cash equivalents and other short-term holdings. For purposes of satisfying the 80% requirement, the fund also may invest in derivative instruments that have economic characteristics similar to such securities.

The fund may invest a substantial portion of its assets in mortgage-related securities, including “sub-prime” mortgages, and asset-backed securities. The fund also may invest a portion of its assets in subordinated debt

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Summary Prospectus

securities, below investment grade debt securities (known as “junk bonds”), securities that are in default, securities of non-U.S. issuers, and event-linked bonds.

The fund may invest up to 20% of its net assets in debt securities rated below investment grade or, if unrated, of equivalent credit quality as determined by the adviser. The fund may invest up to 15% of its total assets in securities of non-U.S. issuers, including up to 5% of its total assets in securities of emerging market issuers.

The fund may invest in securities with a broad range of maturities, and maintains an average portfolio maturity which varies based upon the judgment of the fund's investment adviser. The fund's investments may have fixed or variable principal payments and all types of interest rate payment and reset terms, including fixed rate, floating rate, inverse floating rate, zero coupon, contingent, deferred and payment in kind and auction rate features. The fund's investments may include instruments that allow for balloon payments or negative amortization payments.

The fund may, but is not required to, use derivatives, such as credit default swaps and bond and interest rate futures. The fund may use derivatives for a variety of purposes, including as a hedge against adverse changes in the market price of securities, interest rates or currency exchange rates; as a substitute for purchasing or selling securities; and to increase the fund's return as a non-hedging strategy that may be considered speculative. The fund may choose not to make use of derivatives for a variety of reasons, and any use may be limited by applicable law and regulations. The fund may hold cash or other short-term investments.

The adviser considers both broad economic and issuer specific factors in selecting investments. In assessing the appropriate maturity, credit quality and sector weighting of the fund's portfolio, the adviser considers a variety of factors that are expected to influence economic activity and interest rates. The adviser selects individual securities to buy and sell based upon such factors as a security’s yield, liquidity and rating, an assessment of credit quality, and sector and issuer diversification.

Principal risks of investing in the fund

You could lose money on your investment in the fund. As with any mutual fund, there is no guarantee that the fund will achieve its objectives.

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Market risk. The values of securities held by the fund may go up or down, sometimes rapidly or unpredictably, due to general market conditions, such as real or perceived adverse economic, political, or regulatory conditions, inflation, changes in interest or currency rates or adverse investor sentiment. Adverse market conditions may be prolonged and may not have the same impact on all types of securities. The values of securities may fall due to factors affecting a particular issuer, industry or the securities market as a whole. The stock market may perform poorly relative to other investments. (This risk may be greater in the short term.) The financial crisis that began in 2008 has caused a significant decline in the value and liquidity of many securities of issuers worldwide. Some governmental and non-governmental issuers (notably in Europe) have defaulted on, or been forced to restructure, their debts, and many other issuers have faced difficulties obtaining credit. These market conditions may continue, worsen or spread, including in the U.S., Europe and beyond. Further defaults or restructurings by governments and others of their debt could have additional adverse effects on economies, financial markets and asset valuations around the world. In response to the crisis, the U.S. and other governments and the Federal Reserve and certain foreign central banks have taken steps to support financial markets. The withdrawal of this support, failure of efforts in response to the crisis, or investor perception that these efforts are not succeeding could negatively affect financial markets generally as well as the value and liquidity of certain securities. Whether or not the fund invests in securities of issuers located in or with significant exposure to countries experiencing economic and financial difficulties, the value and liquidity of the fund’s investments may be negatively affected by the countries experiencing these difficulties. In addition, legislation recently enacted in the U.S. is changing many aspects of financial regulation. The impact of the legislation on the markets, and the practical implications for market participants, may not be fully known for some time. The fund may experience a substantial or complete loss on any individual security.

Interest rate risk. Interest rates may go up, causing the value of the fund's investments to decline (this risk generally will be greater for securities with longer maturities).

Credit risk. If an issuer or guarantor of a security held by the fund or a counterparty to a financial contract with the fund defaults on its obligation to pay principal and/or interest, has its credit rating downgraded or is perceived to be less creditworthy, or the credit quality or value of any

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Summary Prospectus

underlying assets declines, the value of your investment will decline. Credit risk is broadly gauged by the credit ratings of the securities in which the fund invests. However, ratings are only the opinions of the companies issuing them and are not guarantees as to quality. Junk bonds have a higher risk of default or are already in default and are considered speculative.

Prepayment or call risk. Many issuers have a right to prepay their securities. If interest rates fall, an issuer may exercise this right. If this happens, the fund will be forced to reinvest prepayment proceeds at a time when yields on securities available in the market are lower than the yield on the prepaid security. The fund also may lose any premium it paid on the security.

Extension risk. During periods of rising interest rates, the average life of certain types of securities may be extended because of slower than expected principal payments. This may lock in a below market interest rate, increase the security's duration (the estimated period until the security is paid in full) and reduce the value of the security.

Liquidity risk. Some securities held by the fund may be difficult to sell, or illiquid, particularly during times of market turmoil. Illiquid securities also may be difficult to value. If the fund is forced to sell an illiquid asset to meet redemption requests or other cash needs, the fund may be forced to sell at a loss.

Portfolio selection risk. The adviser’s judgment about the quality, relative yield, relative value or market trends affecting a particular sector or region, market segment, security or about interest rates generally may prove to be incorrect.

U.S. government agency obligations risk. The fund invests in obligations issued by agencies and instrumentalities of the U.S. government. Government-sponsored entities such as Federal National Mortgage Association (Fannie Mae), Federal Home Loan Mortgage Corporation (Freddie Mac) and the Federal Home Loan Banks (FHLBs), although chartered or sponsored by Congress, are not funded by congressional appropriations and the debt and mortgage-backed securities issued by them are neither guaranteed nor issued by the U.S. government. Such debt and mortgage-backed securities are subject to the risk of default on the payment of interest and/or principal, similar to debt of private

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issuers. Although the U.S. government has provided financial support to Fannie Mae and Freddie Mac in the past, there can be no assurance that it will support these or other government-sponsored entities in the future.

Mortgage-related and asset-backed securities risk. The value of mortgage-related and asset-backed securities will be influenced by factors affecting the housing market and the assets underlying such securities. As a result, during periods of declining asset value, difficult or frozen credit markets, swings in interest rates, or deteriorating economic conditions, mortgage-related and asset-backed securities may decline in value, face valuation difficulties, become more volatile and/or become illiquid. Additionally, during such periods and also under normal conditions, these securities are also subject to prepayment and call risk. Some of these securities may receive little or no collateral protection from the underlying assets and are thus subject to the risk of default. The risk of such defaults is generally higher in the case of mortgage-backed investments that include so-called “sub-prime” mortgages. The structure of some of these securities may be complex and there may be less available information than for other types of debt securities. Upon the occurrence of certain triggering events or defaults, the fund may become the holder of underlying assets at a time when those assets may be difficult to sell or may be sold only at a loss.

Risks of subordinated securities. A holder of securities that are subordinated or “junior” to more senior securities of an issuer is entitled to payment after holders of more senior securities of the issuer. Subordinated securities are more likely to suffer a credit loss than non-subordinated securities of the same issuer, any loss incurred by the subordinated securities is likely to be proportionately greater, and any recovery of interest or principal may take more time. As a result, even a perceived decline in creditworthiness of the issuer is likely to have a greater impact on them.

High yield or “junk” bond risk. Debt securities that are below investment grade, called “junk bonds,” are speculative, have a higher risk of default or are already in default, tend to be less liquid and are more difficult to value than higher grade securities. Junk bonds tend to be volatile and more susceptible to adverse events and negative sentiments.

Risks of non-U.S. investments. Investing in non-U.S. issuers or issuers with significant exposure to foreign markets may involve unique risks compared to investing in securities of U.S. issuers. These risks are more pronounced for issuers in emerging markets or to the extent that the fund

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Summary Prospectus

invests significantly in one region or country. These risks may include different financial reporting practices and regulatory standards, less liquid trading markets, extreme price volatility, currency risks, changes in economic, political, regulatory and social conditions, sustained economic downturns, financial instability, tax burdens, and investment and repatriation restrictions. Lack of information and less market regulation also may affect the value of these securities. Withholding and other non-U.S. taxes may decrease the fund’s return. Non-U.S. issuers may be located in parts of the world that have historically been prone to natural disasters.

Market segment risk. To the extent the fund emphasizes, from time to time, investments in a market segment, the fund will be subject to a greater degree to the risks particular to that segment, and may experience greater market fluctuation than a fund without the same focus.

Risks of investing in floating rate loans. Floating rate loans and similar investments may be illiquid or less liquid than other investments. The value of collateral, if any, securing a floating rate loan can decline or may be insufficient to meet the issuer’s obligations or may be difficult to liquidate. No active trading market may exist for many floating rate loans, and many loans are subject to restrictions on resale. Market quotations for these securities may be volatile and/or subject to large spreads between bid and ask prices. Any secondary market may be subject to irregular trading activity and extended trade settlement periods.

Risks of inverse floating rate obligations. The interest rate on inverse floating rate obligations will generally decrease as short-term interest rates increase, and increase as short-term rates decrease. Due to their leveraged structure, the sensitivity of the market value of an inverse floating rate obligation to changes in interest rates is generally greater than a comparable long-term bond issued by the same issuer and with similar credit quality, redemption and maturity provisions. Inverse floating rate obligations may be volatile and involve leverage risk.

Risks of investing in event-linked bonds. The return of principal and the payment of interest on “event-linked” bonds are contingent on the non-occurrence of a pre-defined “trigger” event, such as a hurricane or an earthquake of a specific magnitude. If a trigger event, as defined within the terms of an event-linked bond, involves losses or other metrics exceeding a specific magnitude in the geographic region and time period specified therein, the fund may lose a portion or all of its accrued interest and/or

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principal invested in such event-linked bond. In addition to the specified trigger events, event-linked bonds may expose the fund to other risks, including but not limited to issuer (credit) default, adverse regulatory or jurisdictional interpretations and adverse tax consequences.

Derivatives risk. Using derivatives can increase fund losses and reduce opportunities for gains when market prices, interest rates or the derivative instruments themselves behave in a way not anticipated by the fund. Using derivatives may increase the volatility of the fund's net asset value and may not provide the result intended. Derivatives may have a leveraging effect on the fund. Some derivatives have the potential for unlimited loss, regardless of the size of the fund’s initial investment. Changes in a derivative’s value may not correlate well with the referenced asset or metric. The fund also may have to sell assets at inopportune times to satisfy its obligations. Derivatives may be difficult to sell, unwind or value, and the counterparty may default on its obligations to the fund. Recent legislation calls for new regulation of the derivatives markets. The extent and impact of the regulation is not yet fully known and may not be for some time. New regulation of derivatives may make them more costly, may limit their availability, or may otherwise adversely affect their value or performance.

Credit default swap risk. Credit default swap contracts, a type of derivative instrument, involve special risks and may result in losses to the fund. Credit default swaps may in some cases be illiquid, and they increase credit risk since the fund has exposure to both the issuer of the referenced obligation and the counterparty to the credit default swap. Swaps may be difficult to unwind or terminate. The swap market could be disrupted or limited as a result of recent legislation, and these changes could adversely affect the fund.

Leveraging risk. The value of your investment may be more volatile and other risks tend to be compounded if the fund borrows or uses derivatives or other investments, such as ETFs, that have embedded leverage. Leverage generally magnifies the effect of any increase or decrease in the value of the fund's underlying assets or creates investment risk with respect to a larger pool of assets than the fund would otherwise have, potentially resulting in the loss of all assets. Engaging in such transactions may cause the fund to liquidate positions when it may not be advantageous to do so to satisfy its obligations or meet segregation requirements.

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Summary Prospectus

Expense risk. Your actual costs of investing in the fund may be higher than the expenses shown in “Annual fund operating expenses” for a variety of reasons. For example, expense ratios may be higher than those shown if overall net assets decrease. Net assets are more likely to decrease and fund expense ratios are more likely to increase when markets are volatile.

Please note that there are many other factors that could adversely affect your investment and that could prevent the fund from achieving its goals.

An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

The fund's past performance

The bar chart and table indicate the risks and volatility of an investment in the fund by showing how the fund has performed in the past. The bar chart shows changes in the performance of the fund's Class A shares from calendar year to calendar year. The table shows the average annual total returns for each class of the fund over time and compares these returns to the returns of the Barclays Capital Aggregate Bond Index, a broad-based measure of market performance that has characteristics relevant to the fund’s investment strategies. You can obtain updated performance information by visiting https://us.pioneerinvestments.com/performance or by calling 1-800-225-6292.

The fund's past performance (before and after taxes) does not necessarily indicate how it will perform in the future.

The bar chart does not reflect any sales charge you may pay when you buy fund shares. If this amount was reflected, returns would be less than those shown.

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Annual return Class A shares (%)

(Year ended December 31)

 

For the period covered by the bar chart:

The highest calendar quarterly return was 6.84% (07/01/2009 to 09/30/2009).
The lowest calendar quarterly return was -3.05% (10/01/2008 to 12/31/2008).

At September 30, 2012, the year-to-date return was 7.47%.

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Summary Prospectus

No performance information is presented for Class K shares in the table because Class K shares do not have annual returns for at least one calendar year. The returns for Class K shares would differ from those of Class A, B, C, R, Y and Z shares because they have different expenses.

Average annual total return (%)

(for periods ended December 31, 2011)

	1 Year	5 Years	10 Years	Since Inception	Inception Date
Class A					10/31/78
Return before taxes	0.35	5.57	5.71	7.61
Return after taxes on distributions	-1.34	3.67	3.82	4.16
Return after taxes on distributions and sale of shares	0.31	3.64	3.76	4.15
Class B	0.10	5.51	5.20	5.28	4/4/94
Class C†	4.18	5.62	5.24	4.87	1/31/96
Class R	4.69	6.19	N/A	5.59	4/1/03
Class Y	5.34	6.86	6.57	6.51	9/20/01
Class Z	5.28	N/A	N/A	7.66	7/6/07
Barclays Capital Aggregate Bond Index (reflects no deduction for fees, expenses or taxes)	7.84	6.50	5.78	8.48	12/31/78

† The performance of Class C shares does not reflect the 1% front-end sales charge in effect prior to February 1, 2004. If you paid a 1% sales charge, your returns would be lower than those shown above.

After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on the investor's tax situation and may differ from those shown. The after-tax returns shown are not relevant to investors who hold fund shares through tax-deferred arrangements such as 401(k) plans or individual retirement accounts.

After-tax returns are shown only for Class A shares. After-tax returns for Class B, Class C, Class K, Class R, Class Y and Class Z shares will vary.

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Management

Investment adviser	Pioneer Investment Management, Inc.
Portfolio management	Kenneth J. Taubes. Executive Vice President and Chief Investment Officer, U.S. of Pioneer (portfolio manager of the fund since 1998), and Charles Melchreit, Vice President of Pioneer (portfolio manager of the fund since 2012).

Purchase and sale of fund shares

You may purchase, exchange or sell (redeem) shares each day the New York Stock Exchange is open through your financial intermediary or, for accounts held directly with the fund, by contacting the fund’s transfer agent in writing or by telephone (Pioneer Investment Management Shareholder Services, Inc., P.O. Box 55014, Boston, MA 02205-5014, tel. 1-800-225-6292).

Your initial investment for Class A or Class C shares must be at least $1,000. Additional investments must be at least $100 for Class A shares and $500 for Class C shares. The initial investment for Class K shares must be at least $5 million. The initial investment for Class Y shares must be at least $5 million. This amount may be invested in one or more of the Pioneer mutual funds that currently offer Class Y shares. There is no minimum additional investment amount for Class K or Class Y shares. There is no minimum investment amount for Class R or Class Z shares. Effective December 31, 2009, Class B shares are no longer offered to new or existing shareholders, except for reinvestment of dividends and/or capital gains distributions and exchanges for Class B shares of other Pioneer funds.

Tax information

The fund intends to make distributions that may be taxed as ordinary income or capital gains.

Payments to broker-dealers and other financial intermediaries

If you purchase the fund through a broker-dealer or other financial intermediary (such as a bank), the fund and its related companies may pay the intermediary for the sale of fund shares and related services. These payments may create a conflict of interest by influencing the broker-dealer or other intermediary

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Summary Prospectus

and your salesperson or investment professional to recommend the fund over another investment. Ask your salesperson or investment professional or visit your financial intermediary’s website for more information.

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Notes

23430-03-1212