Snowball sampling is one of the most popular methods of sampling in qualitative research, central to which are the characteristics of networking and referral. The researchers usually start with a small number of initial contacts (seeds), who fit the research criteria and are invited to become participants within the research. The agreeable participants are then asked to recommend other contacts who fit the research criteria and who potentially might also be willing participants, who then in turn recommend other potential participants, and so on. Researchers, therefore, use their social networks to establish initial links, with sampling momentum developing from these, capturing an increasing chain of participants. Sampling usually finishes once either a target sample size or saturation point has been reached. This entry begins with a description of the conveniences of snowball sampling, followed by some criticisms and limitations of the technique. The next section provides examples of how snowball sampling is used in qualitative research projects. Subsequent sections examine instances in which snowball sampling stalls or fails to produce participants, and offers two examples of cases in which researchers successfully overcame those obstacles. The entry concludes with a look at some variants of snowball sampling that have emerged given technological advances.