This chapter reviews theory and research on intraindividual personality structures and processes. Principles for modeling the architecture of personality, that is, the overall design and operating characteristics of intraindividual personality systems, are addressed. Research demonstrates that a focus on within-person structures and processes advances the understanding of two aspects of personality coherence: the functional relations among distinct elements of personality, and cross-situational coherence in personality functioning that results from interactions among enduring knowledge structures and dynamic appraisal processes. Also reviewed are recent conceptual and empirical advances, which demonstrate that the interindividual personality variables that summarize variability in the population are wholly insufficient for modeling intraindividual personality architecture.