In this commentary we discuss the appropriateness and usefulness of taking into account the dynamic nature of performance when considering the relation between job performance and ratings of job performance. Like the vast majority of research in this area, Murphy (this issue) does not critically examine whether or how changes in ratee performance over time influence job performance ratings. As noted by Murphy and Cleveland (1995), a limitation of performance appraisal research is that it has ignored that employee performance “…is embedded in a context or pattern of employee performance over time” (p. 73). In this commentary, we argue that a consideration of dynamic performance is essential to our understanding of the relation between performance and performance ratings because the dynamic nature of performance (a) affects what raters observe, their utilized integration rules, and ultimately their performance ratings, (b) likely interacts with elements in multi-factor and mediated models (e.g., Murphy, this issue) to influence ratings, and (c) provides useful information about ratee effectiveness. Based on this discussion, we suggest that the dynamic nature of performance should be explicitly addressed in performance measurement systems to strengthen the relation between performance and ratings of performance, and thus increase ratings’ usefulness.