<?xml version="1.0" encoding="us-ascii"?><InstanceReport xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><Version>2.4.0.8</Version><ReportLongName>2101100 - Disclosure - Consolidation and Basis of Presentation</ReportLongName><DisplayLabelColumn>true</DisplayLabelColumn><ShowElementNames>false</ShowElementNames><RoundingOption /><HasEmbeddedReports>false</HasEmbeddedReports><Columns><Column FlagID="0"><Id>1</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelSeparator>

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</LabelSeparator><Level>2</Level><ElementName>us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock</ElementName><ElementPrefix>us-gaap_</ElementPrefix><IsBaseElement>true</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsCalendarTitle>false</IsCalendarTitle><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><PreferredLabelRole>terseLabel</PreferredLabelRole><FootnoteIndexer /><Cells><Cell FlagID="0" ContextID="D2013Q2YTD" UnitID=""><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&lt;div style="font-family:Times New Roman;font-size:10pt;"&gt;&lt;div style="line-height:120%;text-align:left;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;font-weight:bold;"&gt;CONSOLIDATION AND BASIS OF PRESENTATION&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;&lt;br clear="none"/&gt;&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;text-align:justify;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles ("GAAP") for interim financial information and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for annual financial statements. In the opinion of management, the accompanying condensed consolidated financial statements contain all adjustments necessary to present fairly the financial position of National Western Life Insurance Company and its subsidiaries (&amp;#8220;Company&amp;#8221; or "National Western") as of &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;June&amp;#160;30, 2013&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;, and the results of its operations and its cash flows for the &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;for the three and six months ended&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;June&amp;#160;30, 2013&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; and &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;2012&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;. The results of operations for the &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;six&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; months ended &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;June&amp;#160;30, 2013&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; and &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;2012&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; are not necessarily indicative of the results to be expected for the full year. It is recommended that these condensed consolidated financial statements be read in conjunction with the audited consolidated financial statements and notes included in the Company's Annual Report on Form 10-K for the year ended &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;December&amp;#160;31, 2012&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; accessible free of charge through the Company's internet site at &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;text-decoration:underline;"&gt;www.nationalwesternlife.com&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; or the Securities and Exchange Commission internet site at &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;text-decoration:underline;"&gt;www.sec.gov&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;. The condensed consolidated balance sheet at &lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;color:#000000;text-decoration:none;"&gt;December&amp;#160;31, 2012&lt;/font&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt; has been derived from the audited consolidated financial statements as of that date.&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;&lt;br clear="none"/&gt;&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;text-align:justify;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;The accompanying unaudited condensed consolidated financial statements include the accounts of National Western Life Insurance Company and its wholly-owned subsidiaries: The Westcap Corporation, NWL Investments, Inc., NWL Services, Inc., NWL Financial, Inc., NWLSM, Inc. and Regent Care San Marcos Holdings, LLC.  All significant intercorporate transactions and accounts have been eliminated in consolidation.&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;&lt;br clear="none"/&gt;&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;text-align:justify;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;The preparation of financial statements in accordance with U.S. generally accepted accounting principles ("GAAP") requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosures of contingent assets and liabilities, and the reported amounts of revenues and expenses during the reporting periods. Actual results could differ from those estimates. Significant estimates in the accompanying condensed consolidated financial statements include (1) liabilities for future policy benefits, (2) valuation of derivative instruments, (3) recoverability and amortization of deferred policy acquisition costs, (4) valuation allowances for deferred tax assets, (5) other-than-temporary impairment losses on debt securities, (6) commitments and contingencies, and (7) valuation allowances for mortgage loans and real estate.&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;&lt;br clear="none"/&gt;&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;text-align:justify;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;Certain amounts in the prior year condensed consolidated financial statements have been reclassified to conform to the current year presentation.&lt;/font&gt;&lt;/div&gt;&lt;/div&gt;</NonNumbericText><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat></Cell></Cells><ElementDataType>nonnum:textBlockItemType</ElementDataType><SimpleDataType>na</SimpleDataType><ElementDefenition>The entire disclosure for organization, consolidation and basis of presentation of financial statements disclosure.</ElementDefenition><ElementReferences>Reference 1: http://www.xbrl.org/2003/role/presentationRef

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