Chapter 5 is based on the conviction that the problems dealt with in the preceding chapters need to be embedded into the larger multilingual ecologies in which they occur. Since language dominance has proven an important predictor of cross-linguistic influence, which, in turn, determines the acquisition of additional languages, including expectable benefits of previous multilingual experience, one needs to follow up on the factors that are responsible for language dominance. Evidently, these factors are related to or the result of various issues of language policy and planning – both explicit and implicit – that shape the language ecology encountered in a particular region, even down to the nuclear family. It makes a difference whether one studies these issues in traditional European monolingual ecologies where other languages are learnt as classic second or foreign languages, in de jure monolingual ecologies with high numbers of immigrant speakers of other languages, in bilingual territories where the two languages enjoy the same status, coexist peacefully, and where the number of balanced bilinguals is high, in bilingual or multilingual areas with minority languages or stigmatized languages, or in highly multilingual ecologies with a common lingua franca.