The purpose of this paper is to review several quantitative issues and procedures in meta-analysis or research synthesis. Nearly a decade ago, Glass and his colleagues put forth much of the fundamental quantitative methodology in this field. Basically his insight is that many research questions can be answered empirically and quantitatively by a statistical examination of existing studies rather than relying on single studies, opinions. or a priori assertions. Since the original formulations, several useful developments have taken place~that deserve notice. Many of these are attributable to Hedges and others who have further developed the statistical methodology of research synthesis. Other developments can be found in the summarized empirical results of dozens of meta-analyses. Both methodological and substantive developments are treated in this review.