The growth phenomenon is found in practically all the sciences and even in most of the arts, because almost all the objects of human study grow—crystals, molecules, cells, plants, animals, children, personalities, knowledge, ideas, cities, cultures, organizations, nations, wealth, and economic systems. It does not follow, of course, from the mere universality of the growth phenomenon that there must be a single unified theory of growth which will cover everything from the growth of a crystal to the growth of an empire. Growth itself is not a simple or a unified phenomenon, and we cannot expect all the many forms of growth to come under the umbrella of a single theory. Nevertheless all growth phenomena have something in common, and what is more important, the classifications of forms of growth and hence of theories of growth seem to cut across most of the conventional boundaries of the sciences. In addition there are a great many problems which are common to many apparently diverse growth phenomena.