Structural Equation Modeling (SEM) is a technique that is used to estimate, analyze and test models that specify relationships among variables. This book explains the theory behind the statistical methodology, including chapters on conceptual issues, the implementation of an SEM study, and the history of the development of SEM. It provides examples of analyses on biological data including multi-group models, means models, p-technique and time-series. In addition, the book discusses computer applications and contrasts three popular SEM software packages.