The morphology-phonology interface is rife with examples of interactions between the two modules. Various theoretical models have been proposed to either a) cover the entire interface, or b) cover a subset of this interface. Lexical Phonology and Prosodic Phonology are two popular models of how this interface operates. However it is an open question if both models are needed and if one can do the job of the other. In this paper, data from Armenian morpho-phonology shows the need for both models to be combined and used as one single model for the interface. Crucially, data on Armenian stress assignment and destressed vowel reduction necesitates using both Lexical Phonology's concepts of cyclicity and strata and Prosodic Phonology's concepts of prosodic stems and prosodic non-isomorphism.