This is the 2005 edition of a Net Social Expenditure paper that contains information on net (after tax) public and private social expenditure. These indicators supplement the detailed historical information on gross (before tax) publicly mandated social expenditure in the OECD Social Expenditure Database by accounting for the varying roles of voluntary private social spending and the tax system on social policy across OECD countries. Government intervention through the tax system affects social spending as governments levy direct taxes and social security contributions on cash transfers, and indirect taxes on goods and services bought by benefit recipients. In addition, governments may award tax advantages similar to cash benefits and/or grant tax concessions aiming to stimulate the provision of private social benefits. Through compulsion and tax relief public policy contributes to private pension plans, and such arrangements are generally considered within the social domain. This document refines the methodological framework previously developed per earlier editions of net social expenditure and presents indicators based on a common questionnaire for twenty-three OECD countries for which information on taxation of benefits in 2001 is now available: Australia, Austria, Belgium, Canada, the Czech Republic, Denmark, Finland, France, Germany, Iceland, Ireland, Italy, Japan, Korea, Mexico, the Netherlands, New Zealand, Norway, the Slovak Republic, Sweden, Spain, the United Kingdom and the United States. Accounting for the impact of the tax system and private social expenditure leads to a greater similarity in social expenditure to GDP ratios across countries and to a reassessment of the magnitude of welfare states. Usually, Denmark and Sweden are seen as the biggest social spenders. After accounting for the impact of taxation social expenditure to GDP ratios appear highest in France, Germany and Sweden.