The analysis of the stress-dependent harmony systems of Calvello and Servigliano shows that a set of basic typological effects derive from the typological distinction between phonological harmony and morphemic harmony, a distinction determined by the structure of harmonic triggers. Triggers can be morphemes consisting of one or several of features, they can consist of a pure phonological element, or they can be mixed, consisting of both of segmental and floating material. Preservation of underlying contrasts is shown to play a crucial role both in phonological and in morphemic harmony. Several problems and questions that are important for future research are also discussed.