A conceptual and analytic framework for understanding relationships among traits, states, situations, and behaviors is presented. The framework assumes that such relationships can be understood in terms of four questions. (1) What are the relationships between trait and state level constructs, which include psychological states, the situations people experience, and behavior? (2) What are the relationships between psychological states, between states and situations, and between states and behaviors? (3) How do such state level relationships vary as a function of trait level individual differences? (4) How do the relationships that are the focus of questions 1, 2, and 3 change across time? This article describes how to use multilevel random coefficient modeling to examine such relationships. The framework can accommodate different definitions of traits and dispositions (Allportian, processing styles, profiles, etc.) and different ways of conceptualizing relationships between states and traits (aggregationist, interactionist, etc.).