Clusters and stellar angular-momentum evolution

The origin and evolution of stellar rotation has proven to be both important and challenging. Data obtained in star clusters has already provided key constraints on the role of protostellar disks and the timescales for angular-momentum loss and internal transport. Recent data sets also provide empirical support for the idea that a wide range of rotation rates converge on the main sequence. We evaluate the prospects for rotation–mass–age relationships and the role of open clusters in calibrating them.