This paper provides a review of research in consultation. The research is analyzed in terms of future directions, methodological shortcomings, and program emphasis. Input, process and output are suggested as a framework to examine components of consultation. A number of studies are mentioned for each component, and a short summary of the studies is presented. Input variables include consultee and consultant characteristics, and problems presented by the consultee. Process variables include techniques used to encourage the consultee to work on the presenting problems. Outcome variables are those variables that reflect changes resulting from consultation. The following problems and prospects are highlighted: (1) a need for a programmatic research effort; (2) an over-reliance on reports from consultees to validate the effectiveness of consultation; (3) a need for consultation researchers to describe more specifically the consultation process; (4) a need for further work on social influence factors in consultation; (5) a need for research on the acceptability of interventions; (6) a need to develop straightforward, heuristic measures of organizational environment; and (7) a need to study expert consultants in addition to trainees. The paper is followed by an extensive bibliography. (JAZ)