The publication of a new counterinsurgency (COIN) doctrine manual in late 2006 was widely heralded as an indication that the U.S. military was finally coming to understand the problems it has recently faced in Iraq and Afghanistan. However, this interpretation assumes a tight linkage between doctrine as written and operations as actually conducted. By comparing modern counterinsurgency doctrine and operations to those of 1960s, this paper tests and ultimately disproves this proposition. An examination of COIN doctrine and operations in the 1960s reveals that operations seldom matched written doctrine. Instead of winning hearts and minds, improving civil-military relations, conducting small-unit operations, and gathering intelligence, most Vietnam War commanders and units attempted to defeat the insurgency through large-scale operations and overwhelming firepower. Modern U.S. COIN operations in Afghanistan and Iraq demonstrate a similar preference for high-intensity warfare and a similar inability to adapt technologically and mentally to the requirements of COIN. To help explain the discrepancy between written doctrine and actual operations, this paper posits that ingrained organizational concepts and beliefs have a much greater influence on operations than written doctrine. While embedded beliefs can help organizations as they conduct their preferred missions, they can be detrimental in other contexts. Mental and material preparation for high-intensity warfare has made the U.S. military poorly suited to COIN. Altering these beliefs will require more than just new doctrine and some additional professional education: The services must reorient themselves mentally as well as physically.