Statements of the meaning and purpose of physical explanation are numerous. Every philosopher who has written on "Inductive Logic" has in some manner described or circumscribed the problem of physical explanation. The present paper is not a review of existing knowledge or opinions. It was written with an acute consciousness of the incapacity of most theories of explanation to provide grounds upon which modern hypotheses may stand, and it attempts to formulate a concept and an understanding of physical explanation which is, as far as logical principles permit, in conformity with modern views.