This book is devoted to systems theory, one of the themes of contemporary theoretical sociology. A theory, as we know, tries to offer a rational explanation for phenomena in some area of interest (outer space, nature, society and human beings), and makes use of very general, abstract forms of thought, such as concepts, statements, hypotheses, and laws. These abstractions are used to build logically integrated systems of interpretation that in the true sense of the word can be called theories. The important point is that a theory is not a direct and unmediated description of phenomena in the real world, but rather an attempt to identify and interpret a phenomenon’s basic characteristics in idealised and abstract form. Because every instance of scientific research is inherently selective (no research can encompass every aspect of the real world), it is also impossible for any one theory to capture the full complexity of phenomena to which it applies. A theory must therefore somehow manage to reduce this complexity, which is exactly what systems theory, the subject which follows, does.