Recently, a large variety of models considering the protection of critical infrastructures against intentional attacks including defense-attacks strategies have been developed. The current chapter exposes some of the models emphasizing the problems' statements and briefly presenting the solution methodologies. Special focus will be made on intentional attacks and reliability problems with and without full information as well as on network problems. Each of the defender and attacker problems will be explained with alternative objectives of each agent. The use of game theory will be discussed. Moreover, protection tools such as redundancy, deterrence and employment of false targets are also outlined.