After the September 11, 2001 (9/11), attacks on the United States, homeland defense became the primary issue in U.S. defense policy. At the same time, it was clear that homeland defense would have to become a trilateral continental issue, and, thus, would have to include Canada and Mexico. Because the United States and Canada already had developed a relatively close relationship during and after World War II as a result of their common interests and efforts in NATO (North Atlantic Treaty Organization) and NORAD (North American Air Defense), it became important to begin to understand the Mexican armed forces and their capabilities. This monograph, written from a Canadian prospective, is a significant step in that direction. Because interaction among the U.S., Mexican, Canadian, and other hemispheric armed forces is likely to increase, within or outside a continental economic and/or security architecture, better mutual understanding of the structure and inner workings of the not well understood Mexican armed forces is indispensable. Thus, the purpose of this monograph is to provide a long-overdue appraisal of the Mexican armed forces, with the intention of acquainting those in Canada and the United States and other countries in the Western Hemisphere with the Mexican armed forces. This monograph will demonstrate that the armed forces are professional and well respected in Mexico, and that many Mexicans depend on these forces for medical services, physical and human development, and disaster relief. Additionally, the authors expect that this monograph will contribute to a more universal understanding of the history, structure, and doctrine of the Mexican forces, and of the changing nature of civil-military relations in Mexico. This is not only desirable, but likely necessary, as we move further into 21st century interdependence.