Perhaps the most frequently asked question concerning sampling is “What size sample do I need?” The answer to this question is influenced by a number of factors, including the purpose of the study, population size, the risk of selecting a “bad” sample, and the allowable sampling error. Interested readers may obtain a more detailed discussion of the purpose of the study and population size in Sampling the Evidence of Extension Program Impact, PEOD-5 (Israel, 1992). This paper reviews criteria for specifying a sample size and presents several strategies for determining the sample size.