The contents of this volume represent unusually important and lucid contributions to our understanding of the extent to which research, including program evaluation, must be considered a plural enterprise. Chapter One ties together the overall strategies of critical multiplism and meta-analysis and relates them both to generalizability theory. Issues of generalizability are inherently plural. Together, chapters Two and Three show how advantage increases if pluralism is planned and deliberate, whether at the stage of formulating problems and conducting research or at the stage of synthesizing and interpreting the findings of multiple studies. No single study is likely to yield findings that we should consider definitive. The same can probably be said of program evaluations. Certainly no single study can teach us much of what we need to know. Chapter Two, on critical multiplism, describes an overall strategy for the conduct of research. This strategy is applicable to the aggregate efforts of a set of researchers working on problems in common, but it also has implications for the planning of individual research. Chapter Three, on meta-analysis, outlines a strategy for capitalizing on the multiplism achieved by investigators working on a problem whether that multiplism was planned or not. In general, this volume is aimed at helping us to plan our research in a way that maximizes the return on the time and effort that we have invested in it.