Self-energy-functional theory is a formal framework which allows to de-rive non-perturbative and thermodynamically consistent approximations for latticemodels of strongly correlated electrons from a general dynamical variational prin-ciple. The construction of the self-energy functional and the corresponding vari-ational principle is developed within the path-integral formalism. Different clustermean-field approximations, like the variational cluster approximationand cluster ex-tensions of dynamical mean-field theory are derived in this context andtheir mutualrelationship and internal consistency are discussed.