It was once accepted that galaxies form thin disks early: collisional gas with high velocity dispersion should dissipate energy, conserve angular momentum, and develop strong disk-like rotational support in only a few galaxy crossing times (~few hundred Myr). I will present results from our SIGMA survey of star-forming galaxy kinematics at z ~ 2 that challenge this simple picture — disks with strong rotational support were only just beginning to emerge 3 Gyr after the Big Bang. Combining SIGMA with a lower redshift sample from the DEEP2 survey, I will show how rotational-support develops in galaxies from z~2 to now. By the present day, nearly all massive (log M* > 9.5) star-forming galaxies have assembled a rotationally-supported disk. These results reveal the progressive and mass-dependent assembly of disks over the past 10 Gyr.