Major photometric monitoring campaigns of star-forming regions in the past decade have provided rich rotation period distributions of pre-main-sequence stars .
The rotation periods span more than an order of magnitude in period , with most falling between 1 and 10 days .
Thus the broad rotation period distributions found in 100 Myr clusters are already established by an age of 1 Myr .
The most rapidly rotating stars are within a factor of 2-3 of their critical velocities ; if angular momentum is conserved as they evolve to the ZAMS , these stars may come to exceed their critical velocities .
Extensive efforts have been made to find connections between stellar rotation and the presence of protostellar disks ; at best only a weak correlation has been found in the largest samples .
Magnetic disk-locking is a theoretically attractive mechanism for angular momentum evolution of young stars , but the links between theoretical predictions and observational evidence remain ambiguous .
Detailed observational and theoretical studies of the magnetospheric environments will provide better insight into the processes of pre-main-sequence stellar angular momentum evolution .