A type of research in which a sociologist does not merely observe the activites being studied, but takes an active part in them. The benefit is the insight one gains by becoming an "insider"; the disadvantages include a possible loss of persepctive on the subject as well as the danger of physical or psychological harm.

For example, my sociology professor in college once related the story of a husband and wife team who were conducting a study of prostitution. Their method? She turned tricks, and he was her pimp.