Since December 2006, when Felipe Calderon assumed the office of the President, Mexico has embarked upon the implementation of a culture of law and security that has triggered a war with organized crime involving all sectors of society. This implementation has activated a series of renovations in its armed forces, which remain the most trusted institutions in Mexican society. This Letort Paper contributes to an understanding of the structure, culture, motivators, and the challenges that the Mexican military faces in the 21st century. The Paper also provides a clear picture of doctrinal and structural transformations, adaptations, and improvements that the Mexican armed forces have accomplished over the past 5 years. This Paper discusses how the counternarcotic role of the armed forces has impacted its organization, deployments, and operations, and how it has generated new doctrinal and equipment requirements. The Paper also addresses key areas of national and international concern such as the respect for human rights and and the military justice system. Given Mexico’s importance to the United States as a neighbor, an ally, and as its third largest trading partner, understanding the transformation that the Mexican armed forces are undergoing to foster a culture of law should be of prime concern to all actors—government, private sector, and academia—involved in the decisionmaking process.