A scientific treatment of biodiversity must aim at the development of a generally valid theory, for only in this way, the scientific foundations for pragmatic approaches to the preservation of biodiversity can be worked out. This is also embodied in the “International Convention” on the protection and conservation of biodiversity, which was passed at the United Nations’ conference “Environment and Development” at Rio de Janeiro in 1992, and has meanwhile been ratified by numerous nations. In this article, a definition of the concept “biodiversity” will be given, and partly synonymously used terms, like “variation”, “differentiation”, “diversification”, “heterogeneity”, “variety”, “variability”, “complexity”, and “richness” be differentiated. As matter and energy occur in very different organization forms and on varying hierarchy levels, it is necessary to delimit first those areas in which biodiversity phenomena appear.

An essential prerequisite for a scientific investigation of the diversity of biocoenoses and ecosystems is the theoretical examination of opposing positions: holistic approach versus individualistic approach, deterministic approach versus stochastic approach. Central questions are studied, concerning also ecology in general.

The varying forms of biodiversity can basically be assigned to four different groups: diversity of elements (element pattern of biodiversity), diversity of interactions (dynamic pattern of biodiversity), mechanisms causing diversity (causing pattern of biodiversity), and process of functioning (functional pattern of biodiversity). Examples will be given for each group. “Intrabiocoenotic diversity” includes the diversity of phytocoenoses, zoocoenoses, and synusia. A classification into synusia should follow stratotope, choriotope, and merotope patterns. “Interbiocoenotic diversity”, on the other hand, refers to the diversity of landscape parts (vegetation complexes) and landscapes (vegetation complexes occurring together). Some fundamental relations will be outlined.

On the basis of the comprehensive discussion of biodiversity criteria in the literature, 30 hypotheses on biodiversity will be presented and explained. A final chapter deals with the importance of the theory of biodiversity in applied nature protection. The preservation of biodiversity is a basic component of the survival programme “sustainable development”.