Interest in linguistic alternatives was triggered by Labov’s sociolinguistic studies in the early 1960s, which showed that linguistic variation was not random but systematic. Typically, one of the variants is regarded as the default and the others as deviations. This introduction presents an approach to syntactic variation from the perspective of (non‑)canonicity. It first approaches the term ‘non-canonical’ from a morphological and etymological perspective before outlining the frequency- and the theory-based approaches to the notion. The introduction then defines as a canonical syntactic construction a default which under general circumstances will be chosen with the highest likelihood, while any deviation from the default is called ‘non-canonical’. The paper classifies these deviations into five basic but combinable types. While the status of one variant as default is typically stable in research on syntactic variation, research on syntactic (non‑)canonicity places particular emphasis on the elusive character of canonicity depending on, for instance, the variety, register, or mode of English. Thus, an infrequent deviation from the basic SXV order like topicalisation is clearly non-canonical in Standard British English but may well be canonical in another regional variety like Indian English. An overview of the structure of the volume concludes the introduction.