This volume presents summaries of recent research results on the related subjects of source processes and explosion yield estimation, which are important elements of any treaty verification system. The term Source Processes, in the context of nuclear test monitoring, refers to a wide range of research topics. In a narrow definition, it describes the complex physical phenomena that are directly associated with a nuclear explosion, and the catastrophic deformation and transformation of the material surrounding the explosion. In a broader sense, it includes a host of topics related to the inference of explosion phenomena from seismic and other signals. A further widening of the definition includes the study and characterization of source processes of events other than nuclear, such as earthquakes and, in particular, mining explosions. This latter research is especially important relative to the question of identifying and discriminating nuclear explosions from other seismic events. Explosion Yield Estimation deals with the corresponding inverse problem of inferring explosion source characteristics through analyses of the various types of seismic signals produced by the explosion. This is a complex technical task which has been the focus of some of the most contentious treaty monitoring debates. The current compilation of eight articles on Source Processes and six articles on Explosion Yield Estimation gives a good representation of state-of-the-art research currently being conducted in the broad area of seismic source characterization in the context of nuclear test monitoring.