I wrote my master's thesis in Constraint Programming. The textbook for my CP course was Apt's "Principles of Constraint Programming"[1], but I have to admit to barely using it. Most of the books and "introductions" to CP which I've read have been lacking in either rigor or clarity; many important details are glossed over, partly I think, because of CP's development from other kinds of optimization/satisfaction programming. When learning, I mostly used lecture notes from Christian Schulte (from KTH in Sweden) and Pierre Flener (from Uppsala University, also in Sweden). I can unfortunately not find these accessible online at the moment.
