Operations Research Techniques in Constraint Programming Willem-Jan van Hoeve Abstract: In this thesis we investigate the application of efficient operations research techniques in constraint programming for solving NP-complete combinatorial problems. Such problems often occur in practice, for example in logistics. In constraint programming, combinatorial problems are being solved by systematic search in combination with so-called propagation. Propagation reduces the search space, based on the constraints of the problem. We have applied operations research techniques during search as well as propagation. In particular, we present a generic method to apply propagation in case the problem is over-constrained. In such cases we minimize some measure of violation for each constraint. Our method uses graph-theoretic techniques for network flows. We also apply linear and semidefinite relaxations of the problem to speed up the search process. The relaxations are used to find a solution faster and to prove optimality of such solution earlier. Experimental results show the applicability and effectiveness of our method. Keywords: Operations Research, Constraint Programming