Biological diversity on earth is the result of a long process of evolution lasting for more than 3 thousand million years. In very general terms, the evolutionary strategy of living organisms is to optimize of biosphere structure through a balance of its constituent units. Diversity is a quantitative character of these units. That diversity is crucial for the functioning, evolution, stability and safety of the biosphere and these units. Biodiversity can thus be described as a divergent system of basic and derivative levels. As those derivative levels diverge from their base, the links which connect them with each other and with that base become progressively looser. The end point of this "fanning out" of biodiversity is the level of the individual. Biodiversity is thus a dynamic system with very changable units and links. Some investigations now also deal with functional diversity. From this point of view the ecosystem is a basic level and its element is a consortium. At present the biosphere is severely damaged by human activity. Conservation of different types of biodiversity structures should accordingly be based on a systemic multi-functional concept. This means that nature has different properties and values and all of them should be protected. In the immediate future the most important task is to investigate the limits of the biosphere's functional stability and of the ecosystems which make it up. Another very urgent task is to formulate scientific approaches to biodiversity conservation in the different levels. The solution of this problem of biodiversity conservation consists not only in passive forms of protection but also (perhaps even mainly) in the correct usage and the restoration of biological resources. Biodiversity is crucial for survival of humanity: it influences human thought and is of great importance for all human activities at present and in future.