This book is the first to introduce applied behavioral social and health sciences researchers to a new analytic method the timevarying effect model TVEM. It details how TVEM may be used to advance research on developmental and dynamic processes by examining how associations between variables change across time. The book describes how TVEM is a direct and intuitive extension of standard linear regression whereas standard linear regression coefficients are static estimates that do not change with time TVEM coefficients are allowed to change as continuous functions of real time including developmental age historical time time of day days since an event and so forth.The book introduces readers to new research questions that can be addressed by applying TVEM in their research.