This volume contains papers presented at the Workshop on Branching Processes and Their Applications (WBPA09), held in Badajoz, Spain, April 20-23, 2009. These papers deal with theoretical and practical aspects of branching process theory, showing it to be an area of active and interesting research. They clearly indicate the vitality of the theoretical research on this topic, as well as the importance of branching concepts in the development of theoretical approaches to solving new problems in applied fields such as Epidemiology, Cell Kinetics, Genetics, and, of course, Population Dynamics....