This seminar provides researchers with the theoretical framework and hands-on implementation needed to specify, estimate, and interpret complex nonlinear relationships among latent variables in R and Mplus. The nonlinear effects include latent variable interactions, quadratic relationships among latent variables, nonlinear growth, and splines for latent variable models. Participants will learn the statistical frameworks underlying these models and will be provided with reproducible software scripts. The seminar concludes with advice on how to effectively present the results of nonlinear latent variable models. The focus throughout is on application and interpretation of the models.