This United States Marine Corps manual, Marine Corps Reference Publication (MCRP) 6-10.1 Spiritual Fitness Leader's Guide June 2023, is designed to equip leaders with the information needed to understand and lead in spiritual fitness. This will enable leaders to grow in their own spiritual fitness as well as to lead, teach, and facilitate periods of instruction, professional military education, and professional spiritual fitness discussions. This guide provides leaders with evidence-based information that outlines the benefits of spiritual fitness both on an individual and unit level. While the word "spiritual" has historically been associated with religion, spiritual fitness takes a broader perspective and considers religious and non-religious beliefs, principles, and values needed to persevere and prevail. This guide will help leaders understand and communicate the cultural shift that has occurred that defines spirituality as encompassing non-religious and religious belief systems, and that both are approaches to spiritual fitness. This publication complements Marine Corps Tactical Publication (MCTP) 3-30D, Religious Ministry in the United States Marine Corps.