These are notes deriving from lecture courses on the theory of t-designs and graph theory given by the authors in 1973 at Westfield College, London.

Introduction; 1. A brief introduction to design theory; 2. Strongly regular graphs; 3, Quasi-symmetric designs; 4. Strongly regular graphs with no triangles; 5. Polarities of designs; 6. Extension of graphs; 7. Codes; 8. Cyclic codes; 9. Threshold decoding; 10. Reed-Muller codes; 11. Self-orthogonal codes and designs; 12. Quadratic residue codes; 13. Symmetry codes over GF(3); 14. Nearly perfect binary codes and uniformly packed codes; 15. Association schemes; References; Index.