This is the first of a three-volume collection of David Lewis's most recent papers in all the areas to which he has made significant contributions. The purpose of this collection (and the two volumes to follow) is to disseminate even more widely the work of a preeminent and influential late twentieth-century philosopher. The papers are now offered in a readily accessible format. This first volume is devoted to Lewis's work on philosophical logic from the last twenty-five years. The topics covered include: deploying the methods of formal semantics from artificial formalised languages to natural languages, model-theoretic investigations of intensional logic, contradiction, relevance, the differences between analog and digital representation, and questions arising from the construction of ambitious formalised philosophical systems. The volume will serve as an important reference tool for all philosophers and their students.