Address Forms in a Multisystemic Approach: A New Theoretical Model of Analysis. The aim of this paper is to propose a new theoretical model for the analysis of address forms. In the first part of the paper, I do a critical evaluation of existing theoretical models, showing, on the one hand, that the divergent approaches reflect the complexity of address research, and, on the other hand, that there is a need for a unified model to englobe morphosyntactic, semantic, pragmatic, discursive, and diachronic approaches. In the second part of the paper, I present the multisystemic theory developed by the Brazilian linguist Ataliba de Castilho and demonstrate that it can be successfully used for the analysis of address forms. In the last part of the paper, I show that lexicalization, semanticization, discursivization, and grammaticalization (linguistic processes identified by Ataliba de Castilho in his theory) can explain linguistic phenomena of the address systems in Portuguese and Romanian. Keywords: address forms, European Portuguese, Brazilian Portuguese, Romanian, multisystemic theory, multisystemic theory of Ataliba de Castilho