This updated seminal reference provides new Marine officers—and those aspiring to become Marine officers—comprehensive information and guidance on what it takes to become a successful officer of Marines. The ninth edition of the Marine Officer’s Guide includes new content and illustrations to reflect changes in the Department of Defense and the Marine Corps. The book is organized into three parts. After the introductory chapter, Part I addresses the Marine Corps as a military service, an institution, and to some degree, a bureaucracy. This part touches upon the Corps’ storied history; places the service in the nation’s defense and naval establishments, the treatments of which are completely updated; describes its mission, organization, and infrastructure; and reveals inter alia its culture, the sum of its beliefs and ways of thinking, working, and behaving.  Part II concerns topics related to becoming and being an effective officer of Marines. Most important here are discussions of leadership and the profession of arms, but the updated chapters also cover important topics such as unit and individual administration, pay and allowances, and military justice.   Part III provides useful information on personal, family, and social matters. In sum, this new edition of Marine Officer’s Guide is current and applicable to today’s Corps.