This article provides a broad review of the main approaches to evaluation research as they developed over the past six decades. These approaches are the experimental or quasi-experimental approaches of the 1960s and 1970s as epitomised in the work of Donald Campbell and later Thomas Cook; the naturalist and qualitative tradition that challenged the experimental approach in the 1970s and 1980s and illustrated in the works of Guba, Lincoln, Patton and Williams; the critical evaluation approach which found expression in empowerment evaluation as advocated by David Fetterman and responsive evaluation as defended by Robert Stake; Michael Patton's very influential utilisation-focused evaluation of the 1980s and since and the more recent approach of realist evaluation as discussed by Pawson and Tilley. In each case the main tenets of each approach will be discussed.