Nanshi 南史 "History of the South" is a one-book parallel to the the official dynastic histories (zhengshi 正史) of the Southern Dynasties 南朝 (420-589): the Liu-Song 劉宋 (420-479; Songshu 宋書), Southern Qi 南齊 (479-502; Nanqishu 南齊書), Liang 梁 (502-557; Liangshu 梁書), and Chen 陳 (557-589; Chenshu 陳書). Correctly said it is an alternative history (bieshi 別史) and also a multi-dynastic history (tongshi 通史), but belongs nevertheless to the corpus of the dynastic histories because it was of great importance for the reconstruction of the individual dynastic histories.
The Nanshi was compiled by Li Yanshou 李延壽 (fl. 659) and written in a biographic-thematic style (jizhuanti 紀傳體). The part covering the Liu-Song dynasty comprises 3 juan of imperial annals-biographies (benji 本紀), that of the Qi 2 juan, that of the Liang 3 juan, and that of the Chen 2 juan. There are 70 normal and collective biographies (liezhuan 列傳), chronologically divided into these four dynasties.
The collective biographies of imperial consorts (11-12 Houfei zhuan 后妃傳) at the beginning of the normal biographies section include the consorts of all four of the Southern Dynasties, but the rest of the normal biographies, including that of the imperial princes, is arranged chronologically for each of the four ruling houses, each section beginning with the imperial princes of that dynasty: 13-40 Song, 41-44 Qi, 51-54 Liang, and 65-69 Chen. The further collective biographies are those on benevolent officials (70 Xunli zhuan 循吏傳), Confucian scholars (71 Rulin zhuan 儒林傳), writers (72 Wenxue zhuan 文學傳), persons of filial conduct (73-74 Xiaoyi zhuan 孝義傳, including eminent women), scholars in seclusion (75-76 Yinyi zhuan 隱逸傳), imperial favourites (77 Enxing zhuan 恩倖傳), "barbarians" (78-79 Yimo zhuan 夷貊傳), and rebels (80 Zeichen zhuan 賊臣傳).
Li Yanshou's father Li Taishi 李太師 had already recognized that each dynastic history with its biographical arrangement, focused on its own government and state and neglected the history of the counter-dynasties in times when several dynasties claimed the right to rule over (parts of) China. He planned therefore to compile year-by-year annals covering both the Southern and the Northern Dynasties 北朝 (386~581), but these were never completed. His son continued to realize his project and compiled the history of the Southern Dynasties, covering the years from 420 to 589. It was completed in 659.
Parallel to this history he wrote a history of the Northern Dynasties, Beishi 北史. Li Yanshou also took part in the compilation of the offical histories of the Jin dynasty 晉 (265-420), Jinshu 晉書, and the Sui dynasty 隋 (581-618), Suishu 隋書.
Contarily to what his father had planned, the Nanshi and Beishi were not year-by-year chronicles (biannianti 編年體), but once more histories written in the biographic-thematic style used for the official dynastic histories. The advantage of such a historiographical approach is that is is very practical for the study of the genealogies of the eminent families. Although it is a parallel history, the content of the Nanshi is not identical to that of the Songshu, Nanqishu, etc. so that a diligent historian has to study both variants.