  We discuss ergodicity breaking in frustrated disordered systems with no
apparent broken symmetry of the Hamiltonian and present a way how to amend it
in the low-temperature phase. We demonstrate this phenomenon on mean-field
models of spin glasses. We use replicas of the spin variables to test
thermodynamic homogeneity of ergodic equilibrium systems. We show that
replica-symmetry breaking reflects ergodicity breaking and is used to restore
an ergodic state. We then present explicit asymptotic solutions for the Ising,
Potts and $p$-spin glasses. Each of the models shows a different
low-temperature behavior and the way the replica symmetry and ergodicity are
broken.
