1 Introduction

Through the impetus of the BeppoSAX satellite, there is now general agreement that the bursts (or at least a substantial subset of them) are ultraenergetic phenomena, posing a severe theoretical challenge and - irrespective of which detailed model proves correct - involving some fascinating and extreme physical processes. There is now a stronger motivation to develop models in fuller detail. This paper outlines some of the key issues. I shall focus on the burst itself, since the afterglow is being considered by several other speakers.