This book examines the present-day distribution and diachronic evolution of a set of infinitival structures in Spanish, Portuguese and Romanian, making use of extensive corpus data and investigating how pragmatic factors and usage patterns interact with syntax. After a contrastive account of the patterns of clausal subordination in Latin and Romance, the rise of prepositional infinitives is traced through the documented history of the three languages, revealing astonishing parallels in their development. The analysis of the data shows how cognitive principles such as reanalysis and entrenchment combine with parameters such as relevance and usage frequency to cause syntactic change. Beyond providing a genuine explanation for the observed processes in the Romance languages, this study offers new evidence for the existence of language-independent, cross-linguistically applicable principles and mechanisms in language change. Contents: Comparative Romance Linguistics; Spanish, Portuguese, Romanian - Historical syntax - Cognitive, usage-based approach to linguistic change - Corpus-based diachronic analyses - Infinitival constructions: distribution, usage patterns; the interface between syntax, pragmatics and semantics - Explanations for emergence and expansion of prepositional infinitive clauses.