These skillfully written essays are based on the Georg Simmel Lectures delivered by Neil J. Smelser at Humboldt University in Berlin in the spring of 1995. A distillation of Smelser's reflections after nearly four decades of research, teaching, and thought in the field of sociology, the essays identify, as he says in the first chapter, ''. . . some central problematicsthose generic, recurrent, never resolved and never completely resolvable issuesthat shape the work of the sociologist.'' Each chapter considers a different level of sociological analysis: micro (the person and personal interaction), meso (groups, organizations, movements), macro (societies), and global (multi-societal). Within this framework, Smelser covers a variety of topics, including the place of the rational and the nonrational in social action and in social science theory; the changing character of group attachments in post-industrial society; the eclipse of social class; and the decline of the nation-state as a focus of solidarity. The clarity of Smelser's writing makes this a book that will be welcomed throughout the field of social science as well as by anyone wishing to understand sociology's essential characteristics and problems.