This paper examines the hostage policy Goryeo Taejo Wang Geon implemented during the Unification War. In this paper, the hostages during his reign are conveniently divided into domestic and overseas hostages. Domestic hostages were the ones the local forces sent up to Wang Geon, and overseas hostages were the ones involved in Goryeo’s diplomacy. Upon his ascension to the throne, Wang Geon took over the hostages who had been held under the reign of Gung-Ye. Not long after his ascension to the throne, he sent envoys down to each administrative region. Wang Geon also accepted new hostages from the local forces who sent up to Wang Geon in token of their obedience；he had conferred favors on the local powers, many of whom subjugated themselves to Wang Geon. These are what we call domestic hostages. Wang Geon exchanged hostages with Hubaekje. For example, he freed Jin Ho from Hubaekje in exchange for captured Wang Shin. They were not just overseas hostages, but also an unusual form of hostage exchange. King Kyungsoon of Silla sent his cousin Yuryeom up to Goryeo. Wang Geon, in turn, took the overseas hostage Yuryeom, as if he were a domestic hostage. Wang Geon leveraged his hostage policy for positioning Goryeo favorably in the Unification War before its rivals were able to. Wang Geon finally won the Unification War in 936. Then, in an attempt to block what seemed to be a reconstruction movement on the part of Hubaekje, he sent Wang In-Jeok to Hujin(後晉) as a hostage. This hostage policy was aimed at cutting Hujin off from remnants of Hubaekje’s rebellious forces. At long last, Wang Geon was able to complete the unification of the entire Korean peninsula. Indeed, his hostage policy was instrumental in Goryeo’s victory. When it comes to the Gi-in system of Goryeo, the term ‘Gi-in’ is believed to have been a variation from the domestic hostage.