Research on mixed models has been extensive over the most recent decade. This book differs from the authors' previous monographs on longitudinal data in that it focuses on mixed models of a linear, generalized linear and nonlinear type. The book pays attention to recent developments that include diagnostics, semi-parametric methodology, non-normal random effects, multivariate longitudinal data, high-dimensional outcomes, joint modeling of longitudinal and survival data and discrimination and classification based on longitudinal data using mixed models.