 Reichenbach’s doctoral thesis, The Concept of Probability in the Mathematical Representation of Reality (1915b), contains many of the themes that concerned him throughout his life, and anticipated in some detail 21st century philosophical discussions of probability relations between microscopic and macroscopic systems. Indeed, the development of his ideas about causality and probability from 1915 until the end of his life can be seen as a series of reexaminations and reformulations of issues the thesis implicitly posed and the solutions it explicitly offered. 