This document defines probability sampling and describes several probability sampling techniques. It begins by explaining that probability sampling selects subjects with a known probability, giving every unit in the population an equal chance of being selected. It then outlines several specific probability sampling techniques: random sampling, systematic random sampling, stratified random sampling, cluster random sampling, and multi-stage sampling. For each technique, it provides a brief definition and example. The document aims to explain how probability sampling allows researchers to generalize results to the larger population.