The Marine Corps has long provided the Nation with a force adept at rapidly and effectively solving complex, multifaceted, and seemingly intractable security challenges-so much so that "Send in the Marines" connotes both a demand for action and a presumption of success. While the general public may not be conversant with what exactly the Marine Corps is or does, our fellow citizens display an intuitive understanding that in times of trouble the Marines stand ready to do whatever has to be done. In recent years, their confidence has been reinforced by the performance of Marines in toppling the regime in Iraq, eradicating the ensuing endemic violence within that country's al Anbar Province, and in numerous humanitarian assistance operations worldwide. This flexibility and dependability has been captured in the expression, "No better friend, and no worse enemy." We have a long track record of success spanning recently from Al Anbar province, to the Barbary Wars and suppression of the slave trade in the early 19th century. These are complex problems in which purely military solutions will not suffice-because the fundamental causes of the conflict are often a complicated combination of security, economic, political and social issues. What assured littoral access and responding to crisis have in common is that they require forces that are strategically mobile, operationally flexible, and tactically proficient. These three defining traits allow the Marine Corps to meet this standard: our naval character, our high state of mental and material readiness, and an exceptional degree of military professionalism. These capabilities and traits ensure that the Marine Corps can effectively support joint force actions to "prevail in today's wars; ... prevent and deter threats against the United States, its interests, and our allies and partners; and prepare to defend the United States in a wide range of contingencies against state and non-state actors." This third edition of the Marine Corps Operating Concepts (MOC) provides a conceptual guide for current and future force development and experimentation. The ideas put forth in this volume are meant to inspire discussion, debate, and innovation during the capability identification and solution development process. It is built around the premise that sea-based Marines must be organized, trained, and equipped to "engage, respond, and project." In order to meet the Nation's needs, the Marine Corps must enhance its ability to engage with a wider set of partners in order to build capability, forge solid relationships, and promote diplomatic access. At the same time, Marine Corps forces must remain ready to respond to crises-whether natural or man-made. They must also be able to project power-either "soft" or "hard" as the situation requires-from the sea. Collectively, these enhancements will expand the Marine Corps' contribution to preventing conflict, protecting national interests, and assuring overseas access.