In the field of historical code-switching research, English historical linguists have been particularly active, exploring medieval and modern data, but as the history of English provides an enormous range of material, it may not be surprising that they have thus far overlooked at least one important sub-period in the English Middle Ages. This is the period immediately following the Norman Conquest of 1066, when England became increasingly trilingual. This chapter is devoted to the long twelfth century, from the late eleventh century until well into the thirteenth. Although the concept of "long century" seems to have been used less frequently by historical linguists than by historians, there are several recent publications in which a "long twelfth century" appears with reference to the history of English between, approximately, the Norman Conquest and the second quarter of the thirteenth century (e.g. Skaffari 2009;Faulkner 2012b;Kwakkel 2012; cf. Treharne 2012). 2 This designation is particularly appropriate here: we encounter several languages in the material dated to this period, which makes a label such as Early Middle English inadequate, particularly as some of the English is not Middle but, rather, Old Englisheven if copied around 1200.The objective of the present chapter is to provide a linguistically orientated overview of code-switching and other multilingual practices in material from the long twelfth century, with English as one of the languages involved. The growing community of historical code-switching researchers has virtually ignored this period, in spite of its "endemic multilingualism" (Trotter 2003: 84) and the recent efforts of scholars working on medieval language and literature to bring this period into focus (particularly Treharne 2012 and Faulkner 2012b). To fill the gap, the extant material needs to be described and examined, and approaches originating in research on other periods tested further. Only the first few steps can be taken here, as the material and phenomena are more diverse and copious than is often expected of this period. 1 The author wishes to acknowledge the Academy of Finland for supporting the Multilingualism in the Long Twelfth Century project (decision number: 257059). 2 Kwakkel (2012: 79) associates this period with the "Twelfth-Century Renaissance", dating it to 1075-1225Skaffari (2009), following the sub-periodisation employed in the Helsinki Corpus of English Texts, does not consider primary sources from after 1250; and Faulkner (2012b: 275) "provocatively" chooses to start his long twelfth century with a pre-Conquest date, 1042, the beginning of Edward the Confessor's reign. Treharne's (2012) work on a period similar to ours starts from the earlier of the eleventh-century conquests, the Viking one by Cnut, and continues until 1220.Final draft version (without subsequent minor alterations) of Skaffari, Janne. 2018. Code-switching in the long twelfth century. In Pahta, Päivi, Janne Skaffari & Laura Wright (eds.).