This book aims to identify lessons learned for future Security Force Assistance efforts by studying America's advisory mission in South Korea. After the invasion of South Korea by North Korea on 25 June 1950, the Republic of Korea (R.O.K.) Army lay shattered and dispersed across South Korea. Embedded Korean Military Advisory Group (KMAG) advisers salvaged remnants of the R.O.K. Army from total defeat and from 1950-1953 KMAG worked diligently to recruit, train, and equip a twenty-division army comprising 576,000 personnel capable of modern combined arms warfare. South Korea served as the United States' first large scale advisory mission and may provide lessons learned for future Security Force Assistance efforts. Fifty years after the Korean War, America finds itself in another large-scale Security Force Assistance mission in Iraq. The insights gained from comparing KMAG and the Iraq advisory mission may provide the current force a better appreciation of the intricacies involved with advising foreign forces in the future.