Previous research on within-person variability in performance has largely examined short-term fluctuations and long-term changes in performance separately. The present study proposes a model—based on the cognitive-affective personality system meta-theory (Mischel & Shoda, 1995)—that integrates short-term and long-term performance variability within the 1 framework. Key propositions of the model include that short-term performance fluctuations are contingent on variability in situational cues and that situational cue–performance contingencies change over time. To test the propositions, performance data for 393 professional male tennis players were analyzed using hierarchical linear modeling. The results showed that 2 types of situational cues—resource allocation cues and task complexity—interact in complex ways to account for short-term performance variability. Moreover, as predicted, the contingency of performance on the situational cues changed over time, highlighting the importance of an integrated approach to short-term and long-term performance variability. The implications of these findings are discussed for studies of performance at work and practical applications that managers can employ to increase work performance. Furthermore, parallels are drawn with previous studies from the broader literature on dynamic job performance.