This United States Marine Corps USMC manual, Marine Corps Tactical Publication MCTP 3-10A Infantry Regiment Operations December 2021, is a new publication that serves as a starting point for understanding the capabilities and considerations of the Marine Corps infantry regiment. This publication serves as the basic reference for infantry regiment operations and is to be used in conjunction with company, battalion, and other Marine Corps doctrine and training publications. This publication is not intended to cover every situation a regimental commander may encounter. It does not address force structure and weapon system changes anticipated over the next several years unless sufficient experimentation and testing have been conducted to generate lessons learned that are ready to be codified here. As such, it does not address concepts for the Marine littoral regiment. This publication is intended for infantry battalion, regimental, and division commanders and their staffs. It is a foundational document that assists in the preparation and execution of regimental-level operations in the current operational environment.