This paper introduces Dynamic Intellectual Investment Trait and State Theory, an extension of Intellectual Investment Trait Theory. Our theory extension (a) centers on dynamic within-person effects of cognitive performance states on intellectual investment personality states and vice versa (i.e., reciprocal effects), (b) integrates within-person dynamics and developmental trajectories in cognitive abilities and intellectual investment traits, and (c) is embedded in a continuous-time modeling framework. Aligning personality theories with statistical models, we discuss the most appropriate model for testing Dynamic Intellectual Investment Trait and State Theory: a continuous-time model that combines dynamics and trends. We apply the Continuous-time Latent Curve Model with Structured Residuals (CT-LCM-SR) in an empirical illustration involving 204 German adults who were assessed roughly 100 times on cognitive abilities (working memory) and intellectual investment personality (interest).