This report, which provides a narrative account of four battles within Operation Inherent Resolve (OIR) and a review of U.S. ground force contributions to those battles, is intended to serve as an operational history and review of warfighting functions as applied to OIR. Although OIR was both a Coalition fight and joint one, the report's focus on U.S. ground forces is meant to address gaps both in analysis and in the common understanding of OIR. This research was structured according to the operational concept of by, with, and through. This concept refers to the U.S. military's reliance on local partners-either a host nation government or a local surrogate force-to prosecute ground fighting with U.S. support. That support typically encompasses U.S. advising and enablers and could involve U.S. forces accompanying the partner. Although the terminology is familiar to those working in national security, it has yet to be formalized in joint doctrine and there are inconsistencies in its usage. The authors trace the development of the concept and its application in OIR, then analyze how it might be better incorporated into military doctrine. The authors detail four battles: the counterattacks on Ramadi and on Fallujah, setting the conditions for Mosul, and the urban fight in Mosul. The choice of these operations was made to ensure treatment of the Euphrates and Tigris river valleys where the Islamic State of Iraq and Syria was defeated in Iraq and to cover battles at different points in the overall campaign.