The introduction of pharmaceuticals and diagnostic agents, as well as disinfectants, into the environmental fields of the water and soil may originate from hospitals and other medical institutions, households (through prescriptions from private physicians), and from animal husbandry or livestock farming and fattening. In addition, these products may also accumulate from the aquaculture (pharmaceutical agents for therapy and prophylaxis, as well as food additives) or may result through the various different manners of employing domestic animals (see Fig. 1). In the following, an attempt will be made to provide some basic considerations and primary viewpoints in more detail with regard to the introduction of pharmaceuticals and diagnostic agents, as well as disinfectants, into the environment. Aside from the legal regulations, the characteristics of the individual substances, their subsequent environmental behavior, the estimated risks involved with these substances, as well as the necessary measures to be taken to solve the problems associated with ‘pharmaceuticals in the environment’ are also considered in depth. In addition to the actual pharmaceutical agents, human and veterinary medicine makes use of a number of other sustances, for example for diagnostic and hygienic purposes. These products will also be included in the following observations.