• Constraint Programming M 
• Mini-CP
• Mini-CP source
• choco 
• MiniZinc 
• gecode
• weeSeepy
• Association for Constraint Programming
• Be-Cool
• The Global Constraint Catalog
• IBM ILOG CPLEX Optimization
• CSPLib
• Edward Tsang, introduction to constraint satisfaction
• CP is rocket science!
• Gene Freuder's CP Anniversary Volume