This chapter provides an overview of the people and financial resources that transit the Mexico–US migration corridor. It shows that as well as the movement of Mexicans to the US, transit and return migration are also relevant. Therefore, the need to overcome the idea of a unidirectional migration corridor. Furthermore, the idea of only one overarching corridor for migrants between Mexico and the US does not do justice to the complex realities of migration trajectories as it obscures complex realities, links, and disruptions taking place in the area. A greater look reveals the existence of multiple and entangled corridors that link specific localities and regions on both sides of the border and stresses the need to consider the often-ignored linkages between internal and international migration. Over the past decades, the diversification of migrant origin regions in Mexico has translated in some cases into an increased diversity of Mexican migrants in destination regions in the US. Importantly, the intensification in border surveillance has severely reduced the traditional circularity of migration from Mexico to the US. Simultaneously, increasing fears of deportation and uncertainty about the future of undocumented Mexicans living in the US result in growing precariousness and vulnerability in migrants’ lives, entailing negative effects on migrants’, their relatives’, and communities’ development options. After this discussion of the complex empirical reality of migration and development in the Mexico–US context, the chapter turns to the three theoretical approaches most often applied to understand development in this corridor. With the aim to provide a complementary overview of authors, the chapter particularly emphasises the work of Mexican migration scholars. First, the chapter discusses neoclassical understandings of the migration–development nexus. Often understood as the perspective of the Global North and promoted by international development agencies, it focuses on the potential of remittances to enhance development in countries of migrants’ origin. Second, it addresses neo-Marxist and structural critiques of the relationship between migration and development, which are often labelled as the perspective from the Global South. It draws on structuralist and dependency-theory related approaches to argue that underdevelopment is a result of core (US) and periphery (Mexico) relations. Third, the chapter shows how that the US–Mexican case has been particularly relevant for the development of the transnational paradigm.