  We study the effects of rotation on the outer convective zones of massive
stars. We examine the effects of rotation on the thermal gradient and on the
Solberg--Hoiland term by analytical developments and by numerical models.
Writing the criterion for convection in rotating envelopes, we show that the
effects of rotation on the thermal gradient are much larger and of opposite
sign to the effect of the Solberg-Hoiland criterion. On the whole, rotation
favors convection in stellar envelopes at the equator and to a smaller extent
at the poles. In a rotating 20 Msun star at 94% of the critical angular
velocity, there are two convective envelopes, with the bigger one having a
thickness of 13.2% of the equatorial radius. In the non-rotating model, the
corresponding convective zone has a thickness of only 4.6% of the radius. The
occurrence of outer convection in massive stars has many consequences.
