Large-scale use of performance assessments for individual-level, high-stakes purposes is not widespread, in part because the scores from such assessments are seldom reliable enough for that use. Perhaps the most pervasive cause of this poor reliability is the error variance associated with a Person ×Task interaction. This problem seems quite similar to problems of transfer of learning. The literature on these 2 issues are synthesized to offer an explanation of Person ×Task variability. A research agenda is then proposed based on this literature.