This volume is a selection of the most significant papers Yu,V. Riz­ nichenko wrote during his 30-year career and concerns the development of fundamental problems of seismology. The book is in five parts. The first is devoted to source seismicity. It starts with a chapter on the "elementary unit" of seismicity, viz. the earthquake source. The size of an earthquake is in itself a significant problem in seismology and, is discussed here. The main energetic parameters of the source are consi­ dered, namely, seismic energy, magnitude, seismic moment, geometric size of the main fault, displacements along the fault, and stress drop. The main results of comparison, mutual adjustment and correlations between these parameters are presented. The following chapters are a logical continuation of the first: from an individual earthquake source to a set of earthquakes in space and time, viz. a seismic regime. The chapters convey the now classical principles of seismic regime parametrization and mapping techniques for long-term average seismic activity based on basic principles. How to determine the maximum possible earthquake is a central question. Both the theoretical (or gnostic) and practical i.e. seismic zon­ ing, aspects are considered. Methods of determining and mapping the maximum possible earthquakes are proposed, in particular, by correlating them with seismic activity and, in general, from seismological and other geophysical, geological, geomorphological and geodetical data sets.