At a time when the credibility of social work is again being questioned, this book offers a critical approach to the debate concerning the reliability and validity of the evidence, research and knowledge that underpins professional social work practice. It critiques the notion of 'evidence' and argues that 'knowledge' is a much broader, more appropriate concept to consider. There is analysis of the different components and sources of this knowledge and an exploration of the often discordant interface between practice and knowledge. Finally, it supports the view that knowledge can be actively developed and tested by a range of people.