Meta-analysis is a method of research synthesis. Research synthesis may be defined as a review of primary research on a given topic with the purpose of integrating the findings (e.g., for creating generalizations or resolving conflicts). Research synthesis is central to the scientific enterprise. Without it, the evidence for various alternative hypotheses cannot be properly evaluated and generalizations cannot be reached, thus the advance of the scientific field as well as any potential practical applications are inhibited. Meta-analysis employs specialized techniques for data gathering and analysis developed specifically for the purposes of research synthesis. This chapter reviews the variety of approaches to research synthesis and discusses their relative merits, advantages, limitations, and drawbacks.