The last decade has seen significant progress in the development and specific clinical application of selective psychotropes. The dimensional approach to clinical psychopharmacology views the behavioral targets of psychotropes as phenomena existing on a continuum and as components, in varying degrees, of most psychopathologies. The modern concept of dimension has been used in different contexts. In psychology it has a mathematical sense, whereas in biological psychiatry it is associated more with biological function. This paper reviews these two concepts and the recent models attempting to merge them into one. The heuristic value of the dimensional approach, as well as some of its pitfalls and new avenues of research, are discussed.