Theoretical sampling is a qualitative research method used to gather data that helps develop or refine a theory. Researchers select participants based on their relevance to the emerging concepts, rather than aiming for a representative sample. This approach allows for deeper insights into specific phenomena. In theoretical sampling, data collection continues until the point of saturation is reached, meaning no new information is being discovered. This method is often associated with grounded theory, a systematic approach developed by Barney Glaser and Anselm Strauss in the 1960s, which emphasizes the generation of theory from data.