Speakers who routinely use more than one language may not use any of their languages in ways which are exactly like that of a monolingual speaker. In sequential bilingualism, for example, there is often evidence of interference from the L1 in the L2 system. Describing these interference phenomena and accounting for them on the basis of theoretical models of linguistic knowledge has long been a focus of interest of Applied Linguistics. More recently, research has started to investigate linguistic traffic which goes the other way: L2 interferences and contact phenomena evident in the L1. Such phenomena are probably experienced to some extent by all bilinguals. They are, however, most evident among speakers for whom a language other than the L1 has started to play an important, if not dominant, role in everyday life (Schmid and Köpke, 2007). This is the case for migrants who move to a country where a language is spoken which, for them, is a second or foreign language. We refer to the phenomena of L1 change and L2 interference which can be observed in such situations as language attrition.