The term “Internationalization at Home” and its definition were first introduced in 2001 (Crowther et al 2001). Since then, strongly related and overlapping concepts and definitions have emerged, notably Internationalization of the Curriculum and Campus Internationalization, which have led to confusion over terminology and risk distracting attention from the main job of implementing internationalized curricula. This chapter focuses on the concept and definition of Internationalization at Home. It first critically explores three accepted definitions: 1. Internationalization; 2. Comprehensive Internationalization; and 3. Internationalization of the Curriculum. This is followed by a discussion of three notions which are more contested: the distinction between internationalization at home and abroad; the OECD definition of an internationalized curriculum; and Campus Internationalization. Their similarities to and differences from Internationalization at Home (IaH) are discussed. Next, recent developments in conceptualizing Internationalization at Home and in its implementation are presented. It will be argued that, while Internationalization of the Curriculum is the overarching term, the concept of IaH within that is still valuable in certain contexts and for certain purposes. On the basis of these arguments, it is maintained that the current definition of IaH does not provide sufficient support for those with an interest in internationalizing domestic curricula. The authors therefore propose a new working definition and identify challenges that await those who want to implement Internationalization at Home.