The US military has had a host of successful experiences in counter-guerrilla war, including some distinct successes with certain aspects of the Vietnam War. However, the paradox stemming from America's unsuccessful crusade in the jungles of Vietnam is thisxe2x80x94because the experience was perceived as anathema to the mainstream American military, hard lessons learned there about fighting guerrillas were neither embedded nor preserved in the US Army's institutional memory. The American military culture's efforts to expunge the specter of Vietnam, embodied in the mantra "No More Vietnams," also prevented the US Army as an institution from really learning from those lessons. In fact, even the term "counterinsurgency" seemed to become a reviled and unwelcome word, one that the doctrinal cognoscenti of the 1980s conveniently transmogrified into "foreign internal defense." Even though many lessons exist in the US military's historical experience with small wars, the lessons from the Vietnam War were the most voluminous. Yet these lessons were most likely the least read, because the Army's intellectual rebirth after Vietnam focused almost exclusively on a big conventional war in Europexe2x80x94the scenario preferred by the US military culture. Since the US Army and its coalition partners are currently prosecuting counter-guerrilla wars in Iraq and Afghanistan, it is useful to revisit the lessons from Vietnam and other counterinsurgencies because they are germane to the wars of today and tomorrow. Capturing all or many of these lessons is beyond the scope of this article and is most likely beyond the scope of a single-volume book. However, this article aims to distill some of the more relevant counterinsurgency lessons from the American military's experiences during Vietnam and before. A bigger goal of this article, however, is to highlight some salient studies for professional reading as the US Army starts to inculcate a mindset that embraces the challenges of counterinsurgency and to develop a culture that learns from past lessons in counterinsurgency. This analysis also offers a brief explanation of US military culture and the hitherto embedded cultural obstacles to learning how to fight guerrillas. To simplify and clarify at the outset, the terms counterinsurgency, counter-guerrilla warfare, small war, and asymmetric conflict are used interchangeably. It is a form of warfare in which enemies of the regime or occupying force aim to undermine the regime by employing classical guerrilla tactics. For most of the 20th century, the US military culture (notwithstanding the Marines' work in small wars) generally embraced the big con#ventional war paradigm and fundamentally eschewed small wars and insurgencies. Thus, instead of learning from our experiences in Vietnam, the Philippines, the Marine Corps' experience in the Banana Wars, and the Indian campaigns, the US Army for most of the last 100 years has viewed these experiences as ephemeral anomalies and aberrationsxe2x80x94distractions from preparing to win big wars against other big powers. As a result of marginalizing the counterinsurgencies and small wars that it has spent most of its existence prosecuting, the US military's big-war cultural preferences have impeded it from fully benefitingxe2x80x94studying, distilling, and incorporating into doctrinexe2x80x94from our somewhat extensive lessons in small wars and insurgencies. This article starts by briefly examining some of the salient lessons for counterinsurgency from Vietnam and lists some of the sources for lessons from that war that have been neglected or forgotten. This article also examines some sources and lessons of counterinsurgencies and small wars predating Vietnam.