Code-switching (CS) refers to the use of two or more languages in the same interaction. Studies on CS have been abundant since the 1970s, and CS has been approached from several different perspectives, which has led to a scattered field with diverse methodologies and terminological debates. In spite of this, recuring patterns of CS have been identified, and several linguistic and extralinguistic factors have been found to affect the formation and distribution of these patterns. Unlike many other language contact phenomena, CS has been regarded as a mostly synchronic form of language contact, in which the linguistic systems stay separate. Some scholars, such as Muysken (2000, 2013) and Matras (2009), have tried to situate CS in the wider context of language contact phenomena. During the last decade, proponents of the usage-based approach to language contact (such as Backus 2013, 2015) have argued for a view that connects the diachronic and synchronic aspects of CS. Nontheless, a more comprehensive framework is needed.