Quasi-alliance refers to the ideation, mechanism and behavior of policy-makers to carry out security cooperation through informal political and security arrangements. As a “gray zone” between alliance and neutrality, quasi-alliance is a hidden national security statecraft. Policy-makers tend to seek a third way to strengthen security cooperation and meanwhile avert the risk of conflict. Based on declassified archives and secondary sources, this book probes the theory and practice of quasi-alliances in the Middle East. Five cases are chosen to test the hypotheses of quasi-alliance formation, management, efficacy and termination, including Anglo-French-Israeli quasi-alliance during the Suez Canal War of 1956; US-Saudi quasi-alliance during the Johnson administration; Soviet-Egypt quasi-alliance during the Sadat administration; and Iran-Syria quasi-alliance since 1979. The research finds that alliance is a hard balancing based on legally binding treaties, while quasi-alliance is a soft balance based on politically binding agreement. The task-oriented quasi-alliance features diversity of functions, flexibility of cooperative means, intangibility of targeting, and limitation of sovereignty transfer.