This field manual establishes doctrine (fundamental principles) for tactical counterinsurgency (COIN) operations at the company, battalion, and brigade level. It is based on lessons learned from historic counterinsurgencies and current operations. This manual continues the efforts of FM 3-24, Counterinsurgency, in combining the historic approaches to COIN with the realities of today's operational environment (OE)-an environment modified by a population explosion, urbanization, globalization, technology, the spread of religious fundamentalism, resource demand, climate change and natural disasters, and proliferation of weapons of mass destruction. This manual is generic in its geographic focus and should be used with other doctrinal sources.