This historical case-study investigates and analyzes how the U.S. Army conducted a multinational operation, and to ascertain any legacies the Boxer Rebellion experiences may provide to the way the U.S. Army conducts multinational operations today. This study is limited to an examination of the multinational operation from an interoperability perspective. The international forces in China are analyzed through the specific functions of command, control, coordination, and liaison as articulated in FM 100-8, The Army in Multinational Operations. The 1900 China Relief Expedition affords an opportunity to reflect upon the U.S. Army's first multinational operation upon entering the twentieth century. The operation was the first opportunity for the Army to join with combined forces in a campaign since French military support provided the decisive edge for victory during the American Revolution. As such, the operation provides a logical starting point when assessing the overall performance of the U.S. Army as it conducted subsequent multinational or combined operations throughout the remainder of the century. The composition of the international expeditionary forces sent to China in response to the Boxer Rebellion posed significant interoperability challenges for the U.S. Army. Every major world power of the twentieth century participated in this endeavor to rescue their citizens held hostage in Peking by the Boxers. Pitted against the Imperial Chinese Army and the Boxers were forces from Austria-Hungary, France, Germany, Great Britain, Italy, Japan, Russia and the United States. Problems such as language differences, coordination, and tactical disparities bedeviled army officers and men. This study discovered that we have little to learn doctrine-wise from the Boxer Rebellion. FM 100-8 codifies the salient points for multinational operations as identified in this study.