Abstract: Stellar ages are notoriously difficult to measure accurately for low-mass
stars, severely limiting our ability to address questions ranging from the
evolutionary state of exoplanets to the chemical history of the Galaxy.
Gyrochronology, which uses stellar rotation as a proxy for age, is a
promising solution to this quandary. Unfortunately, however, theoretical
calibrations of the age-rotation relation have historically been hampered
by the lack of rotational measurements for large numbers of low-mass stars
with a wide range of well-known ages. We are still far from being able to
describe fully the evolution of rotation for low-mass stars, or from being
able to use rotation measurements to estimate accurately the ages of
isolated field stars. I will first summarize recent ground-based and
space-based work to characterize the rotational behavior of G, K, and M
dwarfs in open clusters ranging in age from 125 Myr (the Pleiades) to 3
Gyr (Ruprecht 147), and then compare these data to each other and to
models for stellar spin-down in order to appraise our current
understanding of the age-rotation relation.