Theoretical biology is still in its early stages as an academic discipline. There is even little agreement as to what topics it should deal with or in what manner it should precede; and it is only recently that philosophers felt called upon to notice the relevance of biological topics as evolution or perception to their traditional problems. This work is a publication of the International Union of Biological Sciences, the central organization of all the branches of biology. The main focus here is to explore the possibility of formulating some frame of concepts and methods around which theoretical biology can grow.