This book constitutes the refereeed proceedings of the 6th International Conference on Integer Programming and Combinatorial Optimization, IPCO '98, held in Houston, Texas, USA, in June 1998. The 32 revised papers presented were carefully selected from a total of 77 submissions. The book is divided into sections on O/1 matrices and matroids, edge connectivity, algorithms, integer Programming computation, network flows, scheduling, and quadratic assignment problems.