This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book traces the transformations and philosophical and strategic uses of a concept of problems through medieval, modern and contemporary thought, up to late twentieth-century France. It examines Simondon’s genetic theory of individuation and clarifies the role played therein by a notion of problems. The book turns his attention to an eminent twentieth-century French philosopher outside of the usual canon of “French theory,” Pierre Hadot, known to anglophone scholars primarily through the influence of his studies of antiquity on Foucault’s work on the same period. It reassesses the question of Michel Foucault’s ambiguous relation to psychoanalysis by considering this relation through Foucault’s notion of critique as critical problematization. The book explores the distinction in Gabriel Marcel’s work between problem and mystery, the latter of which Marcel also calls the “meta-problematical”.