A framework is presented for investigating antenna coupling in arbitrary environments by way of antenna and environment scattering parameter matrices. The environment scattering parameter matrices are bona fide scattering parameters that describe the environment when all radiation ports are terminated with nonreflecting loads. Simplification of the antenna coupling equations leads to a second formulation that is compatible with classically-defined antenna scattering parameter matrices. A third formulation, based on an auxiliary set of matrices describing the environment's scattering when all unexcited radiation ports are open-circuited, extends the coupling formulation used in spherical near-field antenna measurements to arbitrary environments.