This training circular, TC 3-21.90 Mortar Platoon Collective Task Publication, is a tool that platoon leaders can use as an aid during training strategy development. The products in this TC are developed to support the battalion's mission plan. This TC provides guidance for platoon leaders, leaders, and Soldiers who are responsible for planning, preparing, executing, and assessing training of the mortar platoon. This publication applies to the Active Army, the Army National Guard (ARNG), Army National Guard of the United States (ARNGUS), and the United States Army Reserve (USAR) unless otherwise stated. The primary target audience for this TC is the platoon leader and other leaders within a mortar platoon. The secondary audience comprises training developers involved in developing training support materials for professional military education. The proponent for this publication is the U.S. Army Training and Doctrine Command. The preparing agency is the U.S. Army Maneuver Center of Excellence.