The widths of weak lines in 656 stars of spectral types on the revised Yerkes Atlas system of Morgan and Keenan have been obtained from plates having a dispersion of 11 A/mm. These line widths have been expressed in terms of v sin i, the projected equatorial velocity required of a rotating, spherical, limb-darkened star in order to reproduce the observed broadening. It seems reasonable that axial rotation is the principal macroscopic broadening agent in those stars less luminous than supergiants, but this is not necessarily the case for the high-luminosity stars. The main conclusions of the pa er are as follows: (1) The mean rotational velocity diminishes through class F, but V sin i values of 20 km sec or greater can be found in types as late as F8 (in luminosity classes II, IV-V, and V) or Go (in classes III and IV). With the exception of two binaries, no stars of type later than G5 have been found with rotationally broadened lines, and the widening in a few single stars of types G2-G5 is marginal. (2) For a given spectral type between F0 and GO, the stars of luminosity classes III and IV have much higher mean rotational velocities than do those of class V. (3) There is no significant difference in the rotational velocities of the weak- and strong-line groups of F- and G-type stars. (4) The luminosity class Ia supergiants have considerably wider lines than do those of class Ib.