Policymakers in welfare democracies throughout the world are raising questions as to whether welfare systems deliver what the public expects, and focus attention on increasing costs. Social workers need more evidence and knowledge about an increasing diversity of social work practices. Users of social welfare are increasingly individualized and made responsible for choosing and delivering their own service through contracts and this makes politicians, social workers and users more interested in evidence and knowledge about social services, even though these interests are often conflicting. These tendencies might be part of the reasons why the evaluation of social work practice seems to be characterized at present by a variety and diversity of research methods, approaches and theories.