Spectroscopic rotational velocities of M, L, and T dwarfs as a function of spectral type. Data taken from Blake et al. (2010); Konopacky et al. (2012); Mohanty & Basri (2003); Reiners & Basri (2008, 2010); Zapatero Osorio et al. (2006). Ultracool dwarfs rotate faster with decreasing temperature (and very likely mass). The 18 targets (star symbols) have a v sini ≥ 30 km s^-1 and spectral types ≥M7. Typical uncertainties of projected rotational velocities (1–3 km s^-1) and upper limits on the rotational velocities of dwarfs warmer than M7 are not plotted for the clarity of the figure. The majority of the M0–M4 dwarfs rotate at speeds below ~3 km s^-1.