This chapter outlines the linguistic properties of Welsh and its historical and sociolinguistic context. It sketches the main features of Welsh phonology, including vowel, diphthong and consonant phoneme inventories, focusing on issues involving vowel length, the complex set of diphthongs, and voiceless nasal consonants, including major dialect differences. Mutation, changes in word-initial consonants triggered by morphosyntactic features, is a characteristic of Welsh that has drawn considerable attention, and both phonological and morphosyntactic aspects of the phenomenon are discussed. In morphology, topics of interest include extensive regular vowel alternation and the formation of the singular–plural distinction. Mildly synthetic verbal morphology sits alongside another typologically significant property, inflection of prepositions for person and number. Major features of Welsh syntax include head-initial and VSO word order, restrictions on finite verbs in complement clauses, an elaborate system of clause-initial particles, and marking of predicate adjectives and nominals with a dedicated predicative particle. A final section looks at current sociolinguistic issues, including changes in the traditional diglossic relationship between literary and spoken Welsh, and changes that are often attributed to language contact and revitalisation.