The predecessor of this book (London Mathematical Society Lecture Note Series 19) had its origin in several short courses of lectures given by the authors at Westfield College, London, in 1973. The audience for the lectures consisted mainly of design theorists, and the aim was to present developments in graph theory and coding theory having a bearing on design theory. An introductory chapter on designs was added, for the benefit of readers without the background of the Westfield audience.

For the present volume, the format has been kept, but extensive revisions and updatings have been made. New material includes ovals in symmetric designs (Chapters 1 and 13), the inequalities of Ray-Chaudhuri and Wilson (Chapter 1), partial geometries, with the Hoffman-Chang and Hall-Connor theorems (Chapter 4), 1-factorisations of K6 (Chapter 8), equidistant codes (Chapter 12), planes and biplanes (Chapter 13), generalised quadratic residue codes and inversive planes (Chapter 14), two-weight projective codes (Chapter 16), and the Krein bound (Chapter 17).