This United States Marine Corps manual, Marine Corps Tactical Publication MCTP 3-40A Health Service Support September 2025, addresses the fundamental principles required for planning and executing Marine air-ground task force health service support activities. This publication provides a broad doctrinal overview for commanders and their staffs regarding health service support tasks and functions related to Marine air-ground task force operations. Additionally, it provides readers with a conceptual understanding of health service support capabilities, planning considerations, command relationships, support requirements, and considerations for the successful execution of missions throughout the competition continuum.