Bergson is rightly considered the philosopher of duration. Has this theory, however, been sufficiently elucidated? Is there a domain, aside from life itself, to which the characteristics of duration can be meaningfully ascribed? Why, in his thesis from 1907, does Bergson write of a “real” duration? His subsequent work Duration and Simultaneity: With Reference to Einstein’s Theory (1922) is the only volume written by Bergson in the period separating Creative Evolution (1907) and The Two Sources of Morality and Religion (1932). Duration and Simultaneity represents a polemical, unique, mature and relatively neglected work, one that allows us however to respond to these questions – provided that we read it as a work of philosophy and metaphysics.   This book was awarded the 2020 Polydore de Paepe Prize of the Royal Academy of Science, Letters and Fine Arts of Belgium.