This chapter presents the motivation and methodology of a cross-linguistic and cross-generational study of DOM in Spanish, Hindi and Romanian as heritage languages. Innovative aspects of this project are the comparison of the same linguistic phenomenon cross-linguistically and in heritage languages that share the same majority language context and the inclusion of adult first generation immigrants to examine the cross-generational component. By including heritage speakers and first-generation immigrants as well as two generations of native speakers in the homeland, we examine whether changes with DOM are observed in both diaspora and homeland contexts, or only in the diaspora context. The purpose of this study was to elucidate the linguistic and situational factors that contribute to DOM erosion within and across languages. The rest of this chapter presents the research questions, more specific hypotheses and the overall methodology.