This is a collection of seven books containing war diaries and drafts of letters and reports written by Yi Sun-sin (1545-1598) during the Imjin Waeran (Japanese Invasion of Korea in 1592), a seven-year war waged between Korea (then Joseon) and Japan triggered by the Japanese invasion of Korea in 1592. It was in 1576 when he was 32 years old that Yi Sun-sin passed the state military examination and started his public career as a low-ranking military official. While Yi was a potent military leader, he was also a talented man of letters and faithful Confucian follower devoted to its virtues such as loyalty and filial piety. Also a capable military strategist and a man of foresight, he foresaw the Japanese invasion while he was serving as a Naval Commander-in-chief for West Jeolla-do and led systematic preparations for war by building battleships and increasing military exercises. With Japan invading Korea in 1592, his meticulous preparations paid off with great historic victories at the battles that ensued one after another at the seas off Okpo (1592), Danghangpo (1592), Hansando (1592), Myeongnyang (1597), and Noryang (1598). After the war, which ended with his heroic death, he was honored with posthumous honorary titles including First-Grade Meritorious Subject of Seonmu (“Bountiful Warrior”) and Chungmu (“Loyal Warrior”). Possessing self-sacrificial patriotism, noble character, and outstanding leadership, Yi Sun-sin played a crucial role in saving Korea from one of its formidable foreign enemies, earning admiration nationwide as one of the greatest heroes in Korean history. The collection consists of seven books titled Imjin Ilgi (“Imjin Year Diary,” 54 pages, from the 5th month in 1592 to the 3rd month the following year), Gyesa Ilgi (“Gyesa Year Diary,” 60 pages, from the 5th month to the 9th month in 1593), Gabo Ilgi (“Gabo Year Diary,” 104 pages, from the 1st to the 7th month in 1594), Byeongsin Ilgi (“Byeongsin Year Diary,” 82 pages, from the 1st to the 10th month in 1596), Jeongyu Ilgi (“Jeongyu Year Diary,” 54 pages, from the 4th to the 10th month in 1597), Jeongyu Ilgi-sok (“Annex to the Jeongyu Year Diary,” 40 pages, from the 8th month in 1597 to the 1st month in 1598), and Musul Ilgi (“Musul Year Diary,” 16 pages, from the 9th to the 10th month in 1598). Yi Sun-sin’s war diaries have been kept by his descendants and were used as a source material for the “War Diary” (Nanjung Ilgi) contained in The Collected Writings by the Loyal Warrior (Chungmugong Jeonseo) published in 1795. The diaries contain valuable information about the military strategies and tactics used by the naval forces during the mid-Joseon period as well as the drafts of the reports sent to the king on the military situations during the Imjin Waeran (Japanese Invasion of Korea in 1592).