This revised working paper examines strategies for interpreting and reporting estimates of intervention effects for subgroups of a study sample. The paper considers why and how subgroup findings are important for applied research, alternative ways to define subgroups, different research questions that motivate subgroup analyses, and the importance of prespecifying subgroups before analyses are conducted. It also considers the importance of using existing theory and prior research to distinguish between subgroups for whom study findings are confirmatory (hypothesis testing), as opposed to exploratory (hypothesis generating), and the conditions under which study findings should be considered confirmatory. Each issue is illustrated by selected empirical examples.