What is logic? What makes it a subject in its own right, separate from (and in the background of) the concerns of other disciplines? What is the distinctive character of a logical term or operation? The wealth of technical developments in all areas of logic in recent years has not diminished the need of serious philosophical reflection on the nature of logic, and indeed there is a growing gap between the logician's work and the philosopher's urge to understand the scope of that work. The aim of this collection is to offer material toward filling that gap. Some of the essays have a programmatic flavour; others put forward articulated views; others still concern themselves with the link between technical aspects and philosophical issues. But all share a common concern for the heart of the problem and stem from a common desire to clarify the nature of the logician's enterprise.