Total-energy local-spin-density energy-band calculations are employed to study the different structural phases (hcp, fcc, and bcc) and magnetic states of Co metal as a function of volume. In the paramagnetic state, the fcc phase is lowest in energy with magnetic order stabilizing the hcp phase as the (observed) ground state. Unlike the case of Mn, Cr, and Fe which have stable antiferromagnetic states in the fcc phase, the ferromagnetic state is the most stable for all three phases of Co.