International audienceThis chapter is dedicated to discussing the engineering aspects involved in the integration of modeling languages, as an essential part of the globalization process. It covers the foundations of language integration, the definition of the relationships between the languages to be integrated, and the various dimensions of language and tool integration. Language variants, evolution, refactoring and retirement are also discussed, as key issues involved in the globalization of modeling languages. Today's software development is characterized by a large degree of improvisation: di↵erent languages and language-based tools are used to create di↵erent artifacts that act on the same (physical or logical) system. Such multiplici...