Complete consensus does not exist regarding what distinguishes unlawful sexual harassment from the legally acceptable expression of sexual feelings, but a decade of litigation has substantially narrowed the area for disputes. In both prima facie and quid pro quo cases, the claimant must prove membership in a protected class, unwelcome sexual harassment based on sex, and a basis for imposing respondeat superior liability. Plaintiffs in quid pro quo cases must also prove that their reaction affected tangible aspects of their terms or privileges of employment. Employers should take affirmative steps to prevent valid claims of harassment. These should include a published polity prohibiting harassment, training for managers and supervisors, and careful procedures in handling complaints. Consistency in the handling of cases is critical.