Abstract The phase-based approach to grammatical derivation and one rooted in the Tree Adjoining Grammar (TAG) formalism share the idea that the derivation of a complex sentence is divided into separate derivations of local domains. These approaches differ, however, in their treatment of syntactic dependencies spanning across such local domains. Under the phase approach, operations in a higher domain can access the edge of a lower domain in accordance with the Phase Impenetrability Condition. In TAG, one local domain can be inserted within another under the adjoining operation. This difference has important consequences for how the locality properties of syntactic dependencies are explained. In this paper, I systematically compare the explanations for locality effects under phases and TAG. I explore the degree to which the explanations offered by these different approaches generalize across A- and A ′ -movement, across different structural contexts, and across the phenomena of displacement and agreement, and whether such generalization is empirically warranted in each case.