Evidence--based practice is an idea whose time has come. Few concepts can have achieved the status of unchallengeable common sense in such a short space of time, and across such a broad range of professional activity. As yet there have been few opportunities to take stock and reflect on the evidence for evidence--based practice, or the implications of its adoption. How effective or feasible is it in medicine? Is it really different? What are the consequences of not basing practice on research? Can evidence--based practice be used in non--clinical settings, where practitioners must deal with the complexity of multi--problem individuals, families and organizations? This text introduces the key concept of Evidence--Based Practice and accounts for its emergence and rapid expansion within and beyond medicine. It then goes on to describe how evidence--based practice is being translated in key areas (medicine, nursing, mental health education and social welfare) while critically appraising the strengths and weaknesses of evidence--based practice as it applies in a range of fields of professional practice.