This article is a corpus-based study on the grammaticalization of the quasi-auxiliary use(d) to. It describes and seeks to explain the historical process whereby use(d) to, starting from the Middle English source construction use ‘be in the habit of’ + to + verb, grammaticalized into a habitual aspect marker with idiosyncratic morphosyntactic properties. A detailed corpus study is presented, based on four historical English corpora, which together cover a time period from 1410 to 2009. The results of the corpus analysis are interpreted within the theoretical framework of usage-based grammar, with the aim of uncovering the mechanisms that propelled the gradual grammaticalization of use(d) to on the semantic, morphological, syntactic and phonological dimensions. Among the underlying mechanisms and processes identified are semantic generalization via host-class expansion and habituation, pragmatic enrichment, analogy, chunking, loss of analyzability and internal structure, as well as phonological reduction through neuromotor automation. Supported by the quantitative empirical evidence from the corpus analysis and drawing on findings from usage-based research on language change, the present study depicts the grammaticalization of use(d) to as a self-feeding process driven by frequency effects, i.e. by the effects that the increasingly high discourse frequency of the use(d) to construction had on its cognitive representation.