Let T be a torus and B a compact T −manifold. Goresky, Kottwitz, and MacPherson show in [GKM] that if B is (what was subsequently called) a GKM manifold, then there exists a simple combinatorial description of the equivariant cohomology ring H * T (B) as a subring of H * T (B T ). In this paper we prove an analogue of this result for T −equivariant fiber bundles: we show that if M is a T −manifold and π : M → B a fiber bundle for which π intertwines the two T −actions, there is a simple combinatorial description of H * T (M ) as a subring of H * T (π −1 (B T )). Using this result we obtain fiber bundle analogues of results of [GHZ] on GKM theory for homogeneous spaces.