For more than three decades, the International Conference on Historical Linguistics (ICHL) has been characterized by diversity, both in terms of the theoretical frameworks used by its researchers and the wide variety of languages that are analyzed. ICHL 18, which took place at the Université du Québec à Montréal in August 2007, was no exception to the continuation of this tradition. The articles in the present volume encompass many different approaches and a wide range of theories, including grammaticalization, generative approaches to linguistic change and variation, reanalysis, the use of analogy, and the interplay between internal and external factors. The volume is divided into four sections, dealing with phonology, with syntax, morphology, and semantics, with external factors in linguistic change, and with tools and methodologies. This way, this volume aims to be a reflection of the diverse trends in current historical linguistic study.