Observational studies of marital interaction have become increasingly popular in recent years, resulting from trends in family research including a movement towards the measurement of behavior rather than attitudes. In fact, there is now a proliferation of coding systems, but no "user's guide" for the researcher. This paper overviews the principal marital observation coding systems, suggests the fundamental characteristics of each, and compares and contrasts the content of the coding systems. Theoretical considerations involved in the use of each coding system are outlined for the five systems, including: (1) the Marital Interaction Coding System; (2) the Couple Interaction Scoring System; (3) the Dyadic Interaction Scoring Code; (4) the Marital and Family Interaction Coding Systems; and (5) the Coding Scheme for Interpersonal Conflict. The appended tables contain comparative information for each of the five coding systems. (Author/JAC)