This method is also a nonexperimental, descriptive type of study. It involves an in-depth descriptive record, kept by an outside observer, of an individual or group of individuals.

In the social sciences this often involves collecting and examining various observations and records of an individual's experiences and/or behaviors. Typical data collected might include biographical data, medical records, family history, observations, interviews, and the results of various psychological tests.

In the natural sciences case studies might involve in-depth studies of a particular animal or group of animals or some detailed investigation of a particular physical phenomenon.