The C.I.M.E. Summer School at Como in 1986 was the first in that series on the subject of combinatorial optimization. Situated between combinatorics, computer science and operations research, the subject draws on a variety of mathematical methods to deal with problems motivated by real-life applications. Recent research has focussed on the connections to theoretical computer science, in particular to computational complexity and algorithmic issues. The Summer School's activity centered on the 4 main lecture courses, the notes of which are included in this volume: