Meta-analysis is a collection of systematic techniques for resolving apparent contradictions in research findings. Meta-analysts translate results from different studies to a common metric and statistically explore the relations between study characteristics and findings. Since G. Glass first used the term "meta-analysis" in 1976, it has become a widely accepted research tool encompassing a family of procedures in a variety of disciplines. Meta-analysis typically follows the same steps as primary research: (1) the purpose is defined; (2) a sample is selected; (3) data are collected and transformed to a common metric (often effect size); and (4) statistical procedures investigate the relationships among study characteristics and findings. Major meta-analytic approaches include vote counting by categorizing findings as positive, negative, or non-significant; classic or Glassian meta-analysis; study effect meta-analysis, with one effect size computed for each study; tests of homogeneity to determine the likelihood that variance among effect sizes is due only to sampling error; and psychometric meta-analysis as recommended by J. E. Hunter and F. L. Schmidt (1990). Four references are listed. (SLD)