12 Months Ended

Mar. 01, 2015

RUSSELL INVESTMENT COMPANY

Supplement dated September 10, 2015 to

PROSPECTUS DATED MARCH 1, 2015

RUSSELL U.S. CORE EQUITY FUND RISK/RETURN SUMMARY:

(i) The following replaces the sub-section entitled “Principal Investment Strategies of the Fund” in the Risk/Return Summary section for the Russell U.S. Core Equity Fund in the Prospectus listed above:

The Fund has a non-fundamental policy to invest, under normal circumstances, at least 80% of the value of its net assets plus borrowings for investment purposes in equity securities economically tied to the U.S. The Fund invests principally in common stocks of large and medium capitalization U.S. companies. The Fund defines large and medium capitalization stocks as stocks of those companies represented by the Russell 1000^® Index or within the capitalization range of the Russell 1000^® Index as measured at its most recent reconstitution. The Fund employs a multi-style (e.g., growth, value, market-oriented, defensive and/or dynamic) and multi-manager approach whereby Russell Investment Management Company (“RIMCo”) allocates a portion of the Fund’s assets among different money managers who employ distinct investment styles. The Fund may implement shifts in its investment style exposures in order to respond to substantial changes in mark risks and opportunities. The Fund employs discretionary and non-discretionary money managers. The Fund’s discretionary money managers select the individual portfolio securities for the assets assigned to them. The Fund’s non-discretionary money managers provide a model portfolio to RIMCo representing their investment recommendations, based upon which RIMCo purchases and sells securities for the Fund. Fund assets not allocated to discretionary money managers include assets managed by RIMCo based upon model portfolios provided by non-discretionary money managers, the Fund’s liquidity reserves and assets which may be managed directly by RIMCo to effect the Fund’s investment strategies and/or to actively manage the Fund’s overall exposures by investing in securities or other instruments that RIMCo believes will achieve the desired risk/return profile for the Fund. RIMCo may use strategies based on indexes that represent the desired exposures, including index replication and optimized index sampling, or utilize quantitative or qualitative analysis or quantitative models designed to assess Fund characteristics and identify a portfolio which provides the desired exposures. The Fund usually, but not always, pursues a strategy to be fully invested by exposing all or a portion of its cash to the performance of appropriate markets by purchasing equity securities and/or derivatives, which typically include index futures contracts. The Fund may also invest in securities of non-U.S. issuers by purchasing American Depositary Receipts (“ADRs”) or Global Depositary Receipts (“GDRs”). Please refer to the “Investment Objective and Investment Strategies” section in the Fund’s Prospectus for further information.

(ii) The following risk factor is added to the sub-section entitled “Principal Risks of Investing in the Fund” in the Risk/Return Summary section for the Russell U.S. Core Equity Fund in the Prospectus listed above:

• Non-Discretionary Implementation Risk. With respect to the portion of the Fund that is managed pursuant to model portfolios provided by non-discretionary money managers, it is expected that trades will be effected on a periodic basis and therefore less frequently than would typically be the case if discretionary money managers were employed. Given that values of investments change with market conditions, this could cause the Fund’s return to be lower than if the Fund employed discretionary money managers with respect to that portion of its portfolio.

RUSSELL U.S. STRATEGIC EQUITY FUND RISK/RETURN SUMMARY:

(i) The following replaces the sub-section entitled “Principal Investment Strategies of the Fund” in the Risk/Return Summary section for the Russell U.S. Strategic Equity Fund in the Prospectus listed above:

The Fund has a non-fundamental policy to invest, under normal circumstances, at least 80% of the value of its net assets plus borrowings for investment purposes in equity securities economically tied to the U.S. The Fund invests principally in common stocks of medium and large capitalization U.S. companies. The Fund defines large and medium capitalization stocks as stocks of those companies represented by the Russell 1000^® Index or within the capitalization range of the Russell 1000^® Index as measured at its most recent reconstitution. The Fund employs a multi-style (growth, value, market-oriented, defensive and dynamic) and multi-manager approach whereby Russell Investment Management Company (“RIMCo”) allocates a portion of the Fund’s assets among different money managers who employ distinct investment styles. The Fund may implement shifts in its investment style exposures in order to respond to substantial changes in mark risks and opportunities. The Fund may employ a limited long-short strategy (also referred to as a 115/15 or 130/30 strategy) pursuant to which it sells securities short. The Fund employs discretionary and non-discretionary money managers. The Fund’s discretionary money managers select the individual portfolio securities for the assets assigned to them. The Fund’s non-discretionary money managers provide a model portfolio to RIMCo representing their investment recommendations, based upon which RIMCo purchases and sells securities for the Fund. Fund assets not allocated to discretionary money managers include assets managed by RIMCo based upon model portfolios provided by non-discretionary money managers, the Fund’s liquidity reserves and assets which may be managed directly by RIMCo to effect the Fund’s investment strategies and/or to actively manage the Fund’s overall exposures by investing in securities or other instruments that RIMCo believes will achieve the desired risk/return profile for the Fund. RIMCo may use strategies based on indexes that represent the desired exposures, including index replication and optimized index sampling, or utilize quantitative or qualitative analysis or quantitative models designed to assess Fund characteristics and identify a portfolio which provides the desired exposures. The Fund usually, but not always, pursues a strategy to be fully invested by exposing all or a portion of its cash to the performance of appropriate markets by purchasing equity securities and/or derivatives, which typically include index futures contracts. The Fund may also invest in securities of non-U.S. issuers by purchasing American Depositary Receipts (“ADRs”) or Global Depositary Receipts (“GDRs”). Please refer to the “Investment Objective and Investment Strategies” section in the Fund’s Prospectus for further information.

(ii) The following risk factor is added to the sub-section entitled “Principal Risks of Investing in the Fund” in the Risk/Return Summary section for the Russell U.S. Strategic Equity Fund in the Prospectus listed above:

• Non-Discretionary Implementation Risk. With respect to the portion of the Fund that is managed pursuant to model portfolios provided by non-discretionary money managers, it is expected that trades will be effected on a periodic basis and therefore less frequently than would typically be the case if discretionary money managers were employed. Given that values of investments change with market conditions, this could cause the Fund’s return to be lower than if the Fund employed discretionary money managers with respect to that portion of its portfolio.

RUSSELL SELECT U.S. EQUITY FUND RISK/RETURN SUMMARY: The following replaces the sub-section entitled “Principal Investment Strategies of the Fund” in the Risk/Return Summary section for the Russell Select U.S. Equity Fund in the Prospectus listed above:

The Fund has a non-fundamental policy to invest, under normal circumstances, at least 80% of the value of its net assets plus borrowings for investment purposes in equity securities economically tied to the U.S. The Fund invests principally in common stocks of large and medium capitalization U.S. companies but may also invest in small capitalization U.S. companies. The Fund defines large and medium capitalization stocks as stocks of those companies represented by the Russell 1000^® Index or within the capitalization range of the Russell 1000^® Index as measured at its most recent reconstitution. Russell Investment Management Company (“RIMCo”) seeks to achieve the Fund’s investment objective by managing the Fund’s overall exposures (such as volatility, momentum, growth, value, quality, defensive, dynamic, capitalization size, industry or sector). RIMCo utilizes a variety of quantitative inputs and qualitative investment information and analysis in the management of the Fund to assess Fund characteristics and identify a portfolio which it believes will provide the desired exposures. After RIMCo has determined the Fund’s desired exposures, RIMCo identifies baskets of stocks and determines their weights within the Fund in order to reflect those desired exposures. These baskets are generally comprised of stocks included in the Russell 1000^® Index but may include or be entirely comprised of stocks not included in the Russell 1000^® Index. The baskets are derived from various indexes (including Russell indexes), quantitative tools and/or rules-based processes designed to achieve desired exposures. RIMCo may also invest in index futures, index put or call options or exchange traded funds as a substitute for the purchase of stocks to achieve desired exposures, in pursuit of the Fund’s investment objective or for hedging purposes. The Fund usually, but not always, pursues a strategy to be fully invested by exposing all or a portion of its cash to the performance of appropriate markets by purchasing equity securities and/or derivatives, which typically include index futures contracts. The Fund may also invest a portion of its assets in securities of companies, known as real estate investment trusts (“REITs”), that own and/or manage properties. Please refer to the “Investment Objective and Investment Strategies” section in the Fund’s Prospectus for further information.

RUSSELL SELECT INTERNATIONAL EQUITY FUND RISK/RETURN SUMMARY: The following replaces the sub-section entitled “Principal Investment Strategies of the Fund” in the Risk/Return Summary section for the Russell Select International Equity Fund in the Prospectus listed above:

The Fund has a non-fundamental policy to invest, under normal circumstances, at least 80% of the value of its net assets plus borrowings for investment purposes in equity securities. The Fund invests principally in equity securities, including common stocks issued by companies economically tied to or located in developed market countries, other than the U.S. The Fund’s securities are denominated principally in foreign currencies and are typically held outside the U.S. The Fund may invest a portion of its assets in equity securities of companies that are economically tied to emerging market countries. The Fund considers the following countries to have developed markets: Australia, Austria, Belgium, Canada, Denmark, Finland, France, Germany, Hong Kong, Iceland, Ireland, Israel, Italy, Japan, Luxembourg, the Netherlands, New Zealand, Norway, Portugal, Singapore, Spain, Sweden, Switzerland, the United Kingdom and the United States. As a general rule, the Fund considers emerging market countries to include every other country. The Fund invests principally in large and medium capitalization companies, but may also invest in small capitalization companies. Russell Investment Management Company (“RIMCo”) seeks to achieve the Fund’s investment objective by managing the Fund’s overall exposures (such as volatility, momentum, growth, value, quality, defensive, dynamic, capitalization size, industry, sector or region). RIMCo utilizes a variety of quantitative inputs and qualitative investment information and analysis in the management of the Fund to assess Fund characteristics and identify a portfolio which it believes will provide the desired exposures. After RIMCo has determined the Fund’s desired exposures, RIMCo identifies baskets of stocks and determines their weights within the Fund in order to reflect those desired exposures. These baskets are generally comprised of stocks included in the Russell Developed ex-U.S. Large Cap Index but may include or be entirely comprised of stocks not included in the Russell Developed ex-U.S. Large Cap Index. The baskets are derived from various indexes (including Russell indexes), quantitative tools and/or rules-based processes designed to achieve desired exposures. RIMCo may also invest in index futures, index put or call options, currency forwards or exchange traded funds as a substitute for the purchase of stocks to achieve desired exposures, in pursuit of the Fund’s investment objective or for hedging purposes. The Fund usually, but not always, pursues a strategy to be fully invested by exposing all or a portion of its cash to the performance of appropriate markets by purchasing equity securities and/or derivatives, which typically include index futures contracts and forward currency contracts. The Fund may use derivatives, including stock options, country index futures and swaps or currency forwards, to (1) manage country and currency exposure as a substitute for holding securities directly or (2) facilitate the implementation of its investment strategy. The Fund may at times seek to protect a portion of its investments against adverse currency exchange rate changes by purchasing forward currency contracts and may engage in currency transactions for speculative purposes. The Fund may also invest a portion of its assets in securities of companies, known as real estate investment trusts (“REITs”), that own and/or manage properties. Please refer to the “Investment Objective and Investment Strategies” section in the Fund’s Prospectus for further information.