First published in 2002. This is Volume VII of seventeen in the Library of Philosophy series on Metaphysics. Written in 1959, after studying Whitehead’s philosophy of applying mathematical logic to physical problems, the author’s main purpose here is to illustrate the two principles upon which the Philosophy of Organism is based, (a) its logical or structural side, and (b) its physical-experiential side. Part I deals with (a) and Part II with (b).