This book sheds light on language variation and change from a generative syntactic perspective, based on a case study of relative clauses in Portuguese and other languages. Concretely, it offers a comparative account of three linguistic phenomena documented in the synchrony and diachrony of Portuguese: remnant-internal relativization, extraposition of restrictive relatives, and appositive relativization. The research methodology adopted involves comparative syntax, both in the diachronic and the synchronic dimensions: Contemporary European Portuguese is systematically compared with earlier stages of Portuguese; moreover, Portuguese is compared with other languages, in particular Latin, English, Dutch, and Italian. The book provides new perspectives on the syntax of relativization. From a theoretical perspective, it shows that competing analyses need not be either false or true universally, but can be instrumental in explaining language variation (both diachronically and synchronically). As for the variation found in the synchronic and diachronic dimensions, it is proposed that languages (and different stages of the same language) might vary according to whether they allow relativization to be derived from specifying coordination. Moreover, the book reports a series of changes that took place in the history of Portuguese after the sixteenth century, which reduced the patterns of nominal discontinuity available in the language.