Since the start of the Islamic conquest of the Maghreb in the 7th century ce, Berber and Arabic have been in continual contact. This has led to large-scale mutual influence. The sociolinguistic setting of this influence is not the same, though; Arabic influence on Berber is found in a situation of language maintenance with widespread bilingualism, while Berber influence on Arabic is no doubt to a large degree due to language shift by Berber speakers to Arabic. Linguistic influence is found on all levels: phonology, morphology, syntax, and lexicon. In those cases where only innovative patterns are shared between the two language groups, it is often difficult to make out where the innovation started; thus the great similarities in syllable structure between Maghrebian Arabic and northern Berber are the result of innovations within both language families, and it is difficult to tell where it started. Morphological influence seems to be mediated exclusively by lexical borrowing. Especially in Berber, this has led to parallel systems in the morphology, where native words always have native morphology, while loans either have nativized morphology or retain Arabic-like patterns. In the lexicon, it is especially Berber that takes over scores of loanwords from Arabic, amounting in one case to over one-third of the basic lexicon as defined by 100-word lists.