The purpose of this thesis is to clearly set forth the relationships which have existed and must still exist between the all embracing science of philosophy and the particular and specialized physical sciences. In order to illustrate this we choose to study something which is, first: necessary to both philosophy and to the natural sciences, and second: that it has a history that may be examined in both its philosophical and scientific aspects over a long period of time. The being which best fulfills these two requirements is the atom. The atom appears in history as far back as the dawn of ancient philosophy, and has continued with it even to the present time. Its importance to the physical sciences need hardly be mentioned, for the modern explanation of a great number of physical phenomena is based upon atomic theories. Its importance in philosophy is shown by the fact that it was introduced into philosophy in an attempt to explain one of the most basic and important problems in philosophy, that is, the problem of change. In order to best fulfill our purpose we shall divide this work into three chapters. The first chapter will be a chronological summary of the different atomic ideas prevailing throughout the history of philosophy and of the problems facing the philosophic atomists. In the second chapter we shall study hylomorphism in order that the reader might understand the Scholastic view of the problem of change. In the third chapter, we shall endeavor to evaluate and co-ordinate the findings of modern physical sciences with the philosophic doctrines of the Schoolmen.