Angular momentum plays a central role in astrophysics through its multiple effects on the formation and evolution of stars, discs, jets, and planets. However, the details of underlying mechanisms are still a matter of debate. This volume offers lectures given by world experts in the field during the Evry Schatzman School on Stellar Physics (EES 2012) held in Aussois, France. It gives the status of the observations showing the presence of rotation in dense cores, accretion disks, jets and stars, and includes theoretical reviews on the mechanisms responsible for angular momentum transport and on the effect it has on these various systems. The latest results are reviewed and discussed extensively. This general review of the angular momentum effects should ease the interpretation of forthcoming data as well as the preparation of observations with the new generation of large interferometers, ALMA and NOEMA, which unprecedented angular resolution will give access to scales that were up to now unreachable and for which angular momentum transport plays acrucial role. Therefore this book will be a valuable reference for researchers and students in the coming years.