Patient expectations have been regarded as a variable affecting the course of psychotherapy for more than 50 years. Yet, even though expectations are often considered a factor common to most psychotherapy systems, their importance may be undervalued. This paper places the expectancy issue in a historical context, discusses the varied definitions of expectancy, and reviews the extant expectancy research literature. Discussion of results affirms the continuing relevance of patient expectations, suggests that they may be even more vital to the psychotherapy process than is often acknowledged, highlights research strengths and weaknesses, and calls attention to areas on which clinicians and researchers might focus to improve treatment effectiveness.