The most important problem in psychology and the social sciences today is the failure to produce cumulative knowledge. This situation has led many to conclude that cumulative knowledge and general principles and theories may be impossible to establish in psychology, a conclusion suggesting that psychology can never be a science--only at best a technology producing answers limited in their applicability to specific situations. This notion has contributed to reductions in funding for research. Psychological researchers have relied on a general two-step procedure to produce cumulative knowledge. First, individual scientists conduct numerous studies; second these studies are integrated subjectively and non-quantitatively, published, and reviewed. However, the information processing task in reviewing a body of studies so that general principles can be drawn from them may be too complex for the unaided human mind. The most important recent development, therefore, is the development of quantitative methods which lift the information processing burden from the reviewer by quantitatively integrating findings across studies, while simultaneously correcting for the effects of statistical and measurement artifacts which distort study findings. Meta-analysis, the term for this process, corrects for the distorting effects of artifacts such as sampling error, measurement unreliability, and range restrictions. The response to these new methods by researchers has been gratifying, as evidenced by meta-analytic studies in journals, books and convention presentations. (JAC)