People typically give up their language when the ecosystem that has sustained it has changed in a way that makes their current vernacular disadvantageous. Some experience the loss after relocating to a new ecosystem that requires knowledge of the host population’s language not only to interact with them but also to be competitive in the new socioeconomic world order. In highly literate societies, a large proportion of the migrants learn the hosts’ language in school, though acquisition of a language by social immersion, through interactions with its practitioners remains the most natural way. It is also thanks to sustained interactions that a language stays alive. In populations where multilingualism is not egalitarian, it will take more than schooling in a disadvantaged language to maintain it. For instance, being able to earn a comfortable living in it will do the trick. For many people, loyalty to the heritage language or mother tongue is outweighed by other pressures from their social ecosystem, for instance feeling integrated in the host population. Also, note that for children the mother tongue need not be the language of at least one of the parents. And when the parents of an immigrant child speak different mother tongues, which of these counts as a heritage language? This is not a simple question to answer. These are some factors, among others, that have worked against the maintenance of some languages in especially cities and diaspora communities. I show in this chapter that the situations are more diverse and defy blanket recommendations.