This volume of 'Mémoires de la SMF' is an extended and revised version of the doctoral thesis of the author defended in 2003 at the University of Orleans. The author proposes a definition of a “measured quantum groupoid“, with an aim to generalize previous work on quantum groups and quantum groupoids, including a duality theorem. The defining axioms given in the volume were later simplified by M. Enock. The presentation is rather technical and the reader is expected to have a solid background in the field. The second part of the book contains a lot of varied examples (including the cases of groupoids, quantum groups, quantum space, quantum groupoids and inclusions of von Neumann algebras).