<?xml version="1.0" encoding="us-ascii"?><InstanceReport xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"><Version>2.2.0.25</Version><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><ReportLongName>0201 - Disclosure - OVERVIEW AND BASIS OF PRESENTATION</ReportLongName><DisplayLabelColumn>true</DisplayLabelColumn><ShowElementNames>false</ShowElementNames><RoundingOption /><HasEmbeddedReports>false</HasEmbeddedReports><Columns><Column><Id>1</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelColumn>false</LabelColumn><CurrencyCode>USD</CurrencyCode><FootnoteIndexer /><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><MCU><KeyName>1/1/2011 - 3/31/2011
USD ($)

USD ($) / shares
</KeyName><CurrencySymbol>$</CurrencySymbol><contextRef><ContextID>FROM_Jan01_2011_TO_Mar31_2011</ContextID><EntitySchema>http://www.sec.gov/CIK</EntitySchema><EntityValue>0001013880</EntityValue><PeriodDisplayName /><PeriodType>duration</PeriodType><PeriodStartDate>2011-01-01T00:00:00</PeriodStartDate><PeriodEndDate>2011-03-31T00:00:00</PeriodEndDate><Segments /><Scenarios /></contextRef><UPS><UnitProperty><UnitID>USD</UnitID><UnitType>Standard</UnitType><StandardMeasure><MeasureSchema>http://www.xbrl.org/2003/iso4217</MeasureSchema><MeasureValue>USD</MeasureValue><MeasureNamespace>iso4217</MeasureNamespace></StandardMeasure><Scale>0</Scale></UnitProperty><UnitProperty><UnitID>Shares</UnitID><UnitType>Standard</UnitType><StandardMeasure><MeasureSchema>http://www.xbrl.org/2003/instance</MeasureSchema><MeasureValue>shares</MeasureValue><MeasureNamespace>xbrli</MeasureNamespace></StandardMeasure><Scale>0</Scale></UnitProperty><UnitProperty><UnitID>EPS</UnitID><UnitType>Divide</UnitType><NumeratorMeasure><MeasureSchema>http://www.xbrl.org/2003/iso4217</MeasureSchema><MeasureValue>USD</MeasureValue><MeasureNamespace>iso4217</MeasureNamespace></NumeratorMeasure><DenominatorMeasure><MeasureSchema>http://www.xbrl.org/2003/instance</MeasureSchema><MeasureValue>shares</MeasureValue><MeasureNamespace>xbrli</MeasureNamespace></DenominatorMeasure><Scale>0</Scale></UnitProperty></UPS><CurrencyCode>USD</CurrencyCode><OriginalCurrencyCode>USD</OriginalCurrencyCode></MCU><CurrencySymbol>$</CurrencySymbol><Labels><Label Id="1" Label="3 Months Ended" /><Label Id="2" Label="Mar. 31, 2011" /></Labels></Column></Columns><Rows><Row><Id>2</Id><IsAbstractGroupTitle>true</IsAbstractGroupTitle><Level>0</Level><ElementName>us-gaap_GeneralPoliciesAbstract</ElementName><ElementPrefix>us-gaap</ElementPrefix><IsBaseElement>true</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><ShortDefinition>No definition available.</ShortDefinition><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsSubReportEnd>false</IsSubReportEnd><IsCalendarTitle>false</IsCalendarTitle><IsTuple>false</IsTuple><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><PreferredLabelRole /><FootnoteIndexer /><Cells><Cell><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText /><NonNumericTextHeader /><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios></Cell></Cells><OriginalInstanceReportColumns /><Unit>Other</Unit><ElementDataType>xbrli:stringItemType</ElementDataType><SimpleDataType>string</SimpleDataType><ElementDefenition>No definition available.</ElementDefenition><IsTotalLabel>false</IsTotalLabel><IsEPS>false</IsEPS><Label>OVERVIEW AND BASIS OF PRESENTATION [Abstract]</Label></Row><Row><Id>3</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><Level>0</Level><ElementName>us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock</ElementName><ElementPrefix>us-gaap</ElementPrefix><IsBaseElement>true</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><ShortDefinition>No definition available.</ShortDefinition><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsSubReportEnd>false</IsSubReportEnd><IsCalendarTitle>false</IsCalendarTitle><IsTuple>false</IsTuple><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><PreferredLabelRole>verboselabel</PreferredLabelRole><FootnoteIndexer /><Cells><Cell><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&lt;p style='margin-top:0pt; margin-bottom:8pt'&gt;&lt;font style="font-family:Arial;font-size:10pt;font-weight:bold;margin-left:0px;"&gt;(&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;font-weight:bold;"&gt;1&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;font-weight:bold;"&gt;)&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;OVERVIEW AND &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;font-weight:bold;"&gt;BASIS OF PRESENTATION&lt;/font&gt;&lt;/p&gt;&lt;p style='margin-top:0pt; margin-bottom:8pt'&gt;&lt;font style="font-family:Arial;font-size:10pt;font-weight:bold;margin-left:0px;"&gt;Overview&lt;/font&gt;&lt;/p&gt;&lt;p style='margin-top:0pt; margin-bottom:8pt'&gt;&lt;font style="font-family:Arial;font-size:10pt;margin-left:0px;"&gt;TeleTech Holdings, Inc. and its subsidiaries (&amp;#8220;TeleTech&amp;#8221; or the &amp;#8220;Company&amp;#8221;) serve their clients through the primary businesses of Business Process Outsourcing (&amp;#8220;BPO&amp;#8221;), which provides outsourced business process, customer management, hosted technology, consulting and marketing services for a variety of industries via operations in the U.S., Argentina, Australia, Belgium, Brazil, Canada, China, Costa Rica, England, Germany, Ghana, Kuwait, Mexico, New Zealand, Northern Ireland, the Philippines, Scotland, South Africa, Spain, Turkey and the United Arab Emirates. &lt;/font&gt;&lt;/p&gt;&lt;p style='margin-top:0pt; margin-bottom:8pt'&gt;&lt;font style="font-family:Arial;font-size:10pt;font-weight:bold;margin-left:0px;"&gt;Basis of Presentation&lt;/font&gt;&lt;/p&gt;&lt;p style='margin-top:0pt; margin-bottom:8pt'&gt;&lt;font style="font-family:Arial;font-size:10pt;margin-left:0px;"&gt;The Consolidated Financial Statements are comprised of the accounts of TeleTech, its wholly owned subsidiaries, its 55% equity owned subsidiary Percepta, LLC, and its 80% interest in&lt;/font&gt;&lt;font style="font-family:Times New Roman;font-size:10pt;"&gt; &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;Peppers &amp;amp; Rogers Group (&amp;#8220;PRG&amp;#8221;) which was acquired on November 30, 2010 (see Note 2 for additional information). &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;All intercompany balances and transactions have been eliminated in consolidation. &lt;/font&gt;&lt;/p&gt;&lt;p style='margin-top:0pt; margin-bottom:8pt'&gt;&lt;font style="font-family:Arial;font-size:10pt;margin-left:0px;"&gt;The accompanying unaudited Consolidated Financial Statements do not include all of the disclosures required by accounting principles generally accepted in the U.S. (&amp;#8220;GAAP&amp;#8221;), pursuant to the rules and regulations of the Securities and Exchange Commission (&amp;#8220;SEC&amp;#8221;). The unaudited Consolidated Financial Statements reflect all adjustments which, in the opinion of management, are necessary to present fairly the consolidated financial position of the Company as of March 31, 2011, and the consolidated results of operations of the Company for the &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;three months ended March 31, 2011&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt; and &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;2010&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;, and the cash flows of the Company for the &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;three months ended March 31, 2011 and 2010&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;. &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;Operating results for the&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt; three months ended March 31, 2010 included a $2.0 million reduction to revenue for disputed service delivery issues which occurred in 2009.&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt; &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;Operating results for the &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;three months ended March 31, 2011&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt; are not necessarily indicative of the results that may be expected for the year ending &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;December 31, &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;2011&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;.&lt;/font&gt;&lt;/p&gt;&lt;p style='margin-top:0pt; margin-bottom:8pt'&gt;&lt;font style="font-family:Arial;font-size:10pt;margin-left:0px;"&gt;These unaudited Consolidated Financial Statements should be read in conjunction with the Company's audited Consolidated Financial Statements and footnotes thereto included in the Company's Annual Report on Form 10-K for the year ended December 31, 2010.&lt;/font&gt;&lt;/p&gt;&lt;p style='margin-top:0pt; margin-bottom:8pt'&gt;&lt;font style="font-family:Arial;font-size:10pt;font-weight:bold;margin-left:0px;"&gt;Use of Estimates&lt;/font&gt;&lt;/p&gt;&lt;p style='margin-top:0pt; margin-bottom:8pt'&gt;&lt;font style="font-family:Arial;font-size:10pt;margin-left:0px;"&gt;The preparation of the Consolidated Financial Statements in conformity with &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;GAAP&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt; requires management to make estimates and assumptions in determining the reported amounts of assets and liabilities, disclosure of contingent liabilities at the date of the Consolidated Financial Statements and the reported amounts of revenue and expenses during the reporting period. On an &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;on&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;g&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;oing&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt; basis, the Company evaluates its estimates including those related to derivatives and hedging activities, income taxes including the valuation allowance for deferred tax assets, self-insurance reserves, litigation&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt; reserves,&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt; restructuring reserves, allowance for doubtful accounts&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt; and valuation of goodwill, long-lived and intangible assets&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities. Actual results may differ materially from these estimates under different assumptions or conditions. &lt;/font&gt;&lt;/p&gt;&lt;p style='margin-top: 0pt; margin-bottom: 0pt;'&gt;&lt;/p&gt;&lt;p style='margin-top:12pt; margin-bottom:8pt'&gt;&lt;font style="font-family:Arial;font-size:10pt;font-weight:bold;margin-left:0px;"&gt;Recently Issued Accounting Pronouncements&lt;/font&gt;&lt;/p&gt;&lt;p style='margin-top:0pt; margin-bottom:8pt'&gt;&lt;font style="font-family:Arial;font-size:10pt;margin-left:0px;"&gt;Effective January 1, 2011, the Company adopted&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt; new revenue guidance that requires an entity to apply the relative selling price allocation method in order to estimate a selling price for all units of accounting, including delivered items when vendor-specific objective evidence or acceptable third-party evidence does not exist. &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;The adoption of this standard did not&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt; have a material impact on &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;the Company's&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt; results of operations, financial position, or cash flows.&lt;/font&gt;&lt;/p&gt;&lt;p style='margin-top:0pt; margin-bottom:8pt'&gt;&lt;font style="font-family:Arial;font-size:10pt;margin-left:0px;"&gt;In December 2010, the FASB issued new guidance related to goodwill impairment testing. The new guidance clarifies the requirements of when to perform step 2 of impairment testing for goodwill for reporting units with zero or negative carrying amounts. &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;The Company adopt&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;ed&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt; this &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;guidan&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;ce on January 1, 2011&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt; and &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;it did&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt; not have a material impact on the Company's results of operations, financial position, or cash flows because the &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;Company has not &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;historically &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;had&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt; or expected to have&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt; a reporting unit with goodwill and a zero or negative carrying amount&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;.&lt;/font&gt;&lt;/p&gt;</NonNumbericText><NonNumericTextHeader>(1)&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;OVERVIEW AND BASIS OF PRESENTATIONOverviewTeleTech Holdings, Inc. and its subsidiaries (&amp;#8220;TeleTech&amp;#8221; or</NonNumericTextHeader><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios></Cell></Cells><OriginalInstanceReportColumns /><Unit>Other</Unit><ElementDataType>us-types:textBlockItemType</ElementDataType><SimpleDataType>string</SimpleDataType><ElementDefenition>Description containing the entire organization, consolidation and basis of presentation of financial statements disclosure. May be provided in more than one note to the financial statements, as long as users are provided with an understanding of (1) the significant judgments and assumptions made by an enterprise in determining whether it must consolidate a VIE and/or disclose information about its involvement with a VIE, (2) the nature of restrictions on a consolidated VIE's assets reported by an enterprise in its statement of financial position, including the carrying amounts of such assets, (3) the nature of, and changes in, the risks associated with an enterprise's involvement with the VIE, and (4) how an enterprise's involvement with the VIE affects the enterprise's financial position, financial performance, and cash flows.  Describes procedure if disclosures are provided in more than one note to the financial statements.</ElementDefenition><ElementReferences>Reference 1: http://www.xbrl.org/2003/role/presentationRef
 -Publisher FASB
 -Name FASB Staff Position (FSP)
 -Number FAS140-4 and FIN46(R)-8
 -Paragraph 8, C1, C7

Reference 2: http://www.xbrl.org/2003/role/presentationRef
 -Publisher AICPA
 -Name Accounting Research Bulletin (ARB)
 -Number 51
 -Paragraph 2-6

Reference 3: http://www.xbrl.org/2003/role/presentationRef
 -Publisher AICPA
 -Name Statement of Position (SOP)
 -Number 94-6
 -Paragraph 10

Reference 4: http://www.xbrl.org/2003/role/presentationRef
 -Publisher FASB
 -Name FASB Interpretation (FIN)
 -Number 46R
 -Paragraph 4, 14, 15

</ElementReferences><IsTotalLabel>false</IsTotalLabel><IsEPS>false</IsEPS><Label>OVERVIEW AND BASIS OF PRESENTATION</Label></Row></Rows><Footnotes /><NumberOfCols>1</NumberOfCols><NumberOfRows>2</NumberOfRows><ReportName>OVERVIEW AND BASIS OF PRESENTATION</ReportName><MonetaryRoundingLevel>UnKnown</MonetaryRoundingLevel><SharesRoundingLevel>UnKnown</SharesRoundingLevel><PerShareRoundingLevel>UnKnown</PerShareRoundingLevel><ExchangeRateRoundingLevel>UnKnown</ExchangeRateRoundingLevel><HasCustomUnits>false</HasCustomUnits><SharesShouldBeRounded>true</SharesShouldBeRounded></InstanceReport>
