United States armed forces have historically fought alongside allied forces, and are currently engaged in several multinational operations around the world. Most, if not all, future U.S. military peacekeeping, combat, or stability operations will continue to consist of multinational structures commonly known as coalitions or alliances. The inherent complexity of creating an effective multinational Command and Control (C2) structure, comprised of different countries and operating under unfamiliar C2 structures, creates tension in achieving unity of effort, unity of command and unity of action towards subsequent mission accomplishment. Historically this tension has revolved around the issue of multinational C2. Differences in national interests, culture, and incompatibilities in operating procedures, technologies, training and operational capabilities add to the tension posed by multinational operations. Fortunately, U.S. Joint, U.S. service, and NATO doctrine, as well as history, provide useful guidelines to ameliorate the tension posed by multinational differences and incompatibilities towards effective multinational C2. A synthesis of the doctrinal foundations of C2 and four historic multinational operations, namely World War I, World War II, the Persian Gulf War, and ISAF, led to the identification of five essential variables that must be addressed and implemented in order to establish effective multinational C2. These variables are the need for establishing unity of purpose through international legitimacy; the need for an integrated multinational command structure in achieving unity of command; the need for an educated human equation; the need for multinational training; and the need for interoperable Communications and Information Systems (CIS) in exercising effective multinational C2. If these five variables are not adequately addressed, then effective multinational C2 will be difficult to achieve. The five essential variables are summarized as follows: (1) T