The object of this book is to provide an account of the results and methods used in combinatorial theories: Graph Theory, Matching Theory, Hamiltonian Problems, Hypergraph Theory, Designs, Steiner Systems, Latin Squares, Coding Matroids, Complexity Theory. In publishing this volume, the editors do not intend to discuss all the classical open problems in combinatorics for which an algebraic approach turns out to be useful. The work is a selection which is intended for specialists, as well as for graduate students who may also be interested in survey papers. The work features a special section which contains a list of unsolved problems proposed by the participants.