Grounded theory was first described by Glaser and Strauss (1967, The discovery of grounded theory: Strategies for qualitative research. Aldine) as the "discovery of theory from data," and describes a group of related methodologies that share key elements of study design and data analysis. Since its inception, grounded theory has evolved into several subtypes with different philosophical underpinnings, the most common of which are post-positivism and constructivism. In post-positivist interpretive frameworks, research is guided by a series of rigorous and logically related steps to identify a single objective underlying reality. In constructivist interpretive frameworks, the researcher strives to understand the meaning participants make of a phenomenon within their social and historical context, recognizing that their own position and perspectives shape their interpretation of their participants' experiences. Grounded theory studies include multiple stages of coding, concurrent collection and analysis of data, constant comparative data analysis, theoretical sampling, and memo-writing to capture researcher reflections and evolving theoretical ideas. The outcome of the study should be a substantive theory that is grounded in the data and describes the phenomenon being studied. Publications relevant to the genetic counseling profession have used a grounded theory approach to investigate a range of topics including patient experiences, professional issues, and genetic counseling education. This article describes the theoretical underpinnings and defining characteristics of grounded theory, provides an overview of post-positivist and constructivist grounded theory approaches, and outlines key elements to consider when conducting and evaluating grounded theory research.