  We consider viscous rotating accretion flows in which most of the viscously
dissipated energy is stored as entropy rather than being radiated. Such
advection-dominated flows may occur when the optical depth is either very small
or very large. We obtain a family of self-similar solutions where the
temperature of the accreting gas is nearly virial and the flow is
quasi-spherical. The gas rotates at much less than the Keplerian angular
velocity; therefore, the central stars in such flows will cease to spin up long
before they reach the break-up limit. Further, the Bernoulli parameter is
positive, implying that advection-dominated flows are susceptible to producing
outflows. Convection is likely in many of these flows and, if present, will
tend to enhance the above effects. We suggest that advection-dominated
accretion may provide an explanation for the slow spin rates of accreting stars
and the widespread occurrence of outflows and jets in accreting systems.
