Marian Smoluchowski is the most frequently cited Polish scientist – Web of Science estimates the number of citations of his works in the period from 1894 to 2014 at 7,235 (Maria Curie-Skłodowska was cited 1,582 times during the same period). Equations relating to the theory of stochastic processes are regularly cited, and Smoluchowski’s continuity equation is used in descriptions of sedimentation and coagulation processes. His research on Brownian motion contributed to the triumph of atomistic theory in physics. Thanks to their use, Richard Zsigmondy, Jean Perrin, and Theodor Svedberg received the Nobel Prize in 1925–1926. The book presents the Polish physicist’s contribution to science and philosophy, especially the philosophy of nature. Smoluchowski’s research on cause and chance led to the introduction of probability calculus into physics. His theory of the criterion of usefulness answers the questions of how science develops and how we verify hypotheses and theories. He proves that usefulness is a universal category and applies to all aspects of human functioning in the natural world.