This book investigates the precise nature of nonfinite structures and explores the ways in which they change. Gary Miller examines a broad range of structures, including traditional infinitives, gerunds, and participles, across different Indo-European (and some non-Indo-European) languages now and in the past. As structures which are nonfinite in some languages are not so in others, the question arises whether the concept 'nonfinite' has any meaning or explanatory power. In seeking an answer to this conundrum, the author shows that infinitives with subject person agreement, such as in West Greenlandic, Modern Greek, Portuguese, Welsh, and Hungarian, share properties with prototypical nonfinite formations. Professor Miller examines languages with morphologically marked tense on infinitives, including Ancient Greek and Latin, and Modern Turkish. He demonstrates that nonfinite structures that can be assigned non-structural (inherent or semantic) case differ systematically from those with either structural or no case. The book concludes with a substantial history of infinitives, gerunds, and participles in Old and Middle English, which reveals why and how nonfinite structures change and vary over time. Gary Miller's innovative theoretical reasoning and the wide range of evidence on which it is brought to bear make this book a considerable contribution to the understanding of grammatical change and its formal expression, as well as to the history of English.