Hypothesis testing involves examination of a sample to say something about the population from which the sample was drawn. An assumption of hypothesis testing is that the sample is representative of the population, at least on the average. This chapter describes the sampling process going from elements in the population to observational units in the sample. There are several methods for selecting the sample. The best of these is probability sampling that leads to different kinds of random samples. Sampling is usually a multistage process and can involve different sampling methods at each stage.