Grounded theory (GT) is a qualitative, explorative, systematic, and data-driven research approach designed to generate a middle-range theory on the studied phenomenon. GT is particularly helpful for examining individual, social psychological, organizational and wider social processes, interaction patterns, and participants' actions, interpretations, and understandings. GT research is also an iterative process, which means that data collection and analysis take place in parallel and inform each other. GT offers a set of rigorous yet flexible guidelines to collect and analyse data. This chapter first traces the development of GT and its versions. From a constructivist GT perspective, it then examines the role of the literature review. Moving on to data collection, the chapter emphasizes the central role of theoretical sampling in GT and considers the various stages of coding and the function of memo-writing throughout the research process. It ends by considering criteria for quality in GT studies.