In work organizations of all sorts (e.g., private sector, public sector, military), it is useful and often necessary to measure the performance and effectiveness of individuals and teams. This measurement is usually done via performance appraisals that are based largely on the judgments of supervisors, peers, customers, or some other evaluators. Other methods might be used to measure job performance (e.g., objective productivity counts), but measures based on judgments and subjective evaluations of performance are much more common. Supervisory performance appraisals are virtually universal in public-sector organizations (except in specific circumstances in which union contracts or regulations call for other approaches), and they are used in the great majority of moderately large and large organizations. They are less likely to be formalized in small businesses, but even in small organizations, it is common to provide employees with annual feedback about their performance and effectiveness.Performance appraisals are often an important factor in decision about pay, promotion, and developmental opportunities (Landy & Conte, 2007). They are an important (but not always welcome) source of feedback (Cleveland, Murphy, & Lim, 2007;Kluger & DeNisi, 1996;Leung, Su, & Morris, 2001). Performance appraisals are often at the heart of equal employment litigation, particularly in cases in which a plaintiff claims to have been evaluated unfairly (Barrett & Kernan, 1987;Cascio & Bernardin, 1981). They are widely used as criteria for validating personnel tests (Landy & Farr, 1980).Performance appraisal represents a method of measurement that depends on informed evaluative judgments (Milkovich & Wigdor, 1991). That is, performance appraisal systems are usually designed around the assumption that the judges who are called on to evaluate performance (the term raters is used here) have access to information about the performance of the individuals they evaluate (ratees) and have an understanding of the appropriate standards that should be used in determining whether performance is adequate, exemplary, or inadequate. Substantial bodies of research have examined the extent to which each of these assumptions is met (Milkovich & Wigdor, 1991), and it has been shown that appraisal systems that depend on raters who are uninformed or whose judgments cannot be trusted or calibrated are unlikely to provide good measures of performance.There is a long history of dissatisfaction and concern with performance appraisal (