Zizhi tongjian bu 續資治通鑑補 "Supplement to the Comprehensive Mirror to Aid in Government", also called Zizhi tongjian buzheng 資治通鑑補正, is a supplement to Sima Guang's 司馬光 (1019–1086) history Zizhi tongjian 資治通鑑. It was written by Yan Yan 嚴衍 (1575-1645, courtesy name Yongsi 永思, style Wuting 午亭). Yan was very interested in history, and it took him thirty years to compile his 294-juan long supplement to the great Zizhi tongjian.
Yan Yan's main sources were the official dynastic histories, but also other historiographical books. His greatest contribution is a critical analysis of Sima Guang's text and the commentary of Hu Sanxing 胡三省. He eliminated errors and added missing sentences and paragraphs. His additions are twofold: one type of addition refers to the main text (bu zhengwen 補正文) and adds short information to it, while other additions provide a thoroughly new text. The latter was added at the end of the main chapters, while the first were added interstitially.
The second type of addition (bu fenzhu 補分注) can be rated as not really historiographically (story instead of history), but was still condidered as interestingly enough to be mentioned. This information is provided in appendixes (fulu 附錄) added at the end of each chapter. In a text-critical part (beikao 備考), Yan Yan provided text passages in some sources that differ from the text in the Zizhi tongjian. Similarly, Hu Sanxing's commentary is supplemented by Yan Yan's addition (buzhu 補注).
Yan Yan in some places altered the reign mottos (nianhao 年號) used in the Zizhi tongjian, where he believed them inappropriate.
The Buzheng was printed in 1851 by Master Tong 童氏 from Jiangxia 江夏, in 1876 by Chen Xuanhuai 盛宣懷 from Piling 毗陵 in a revised version, and in 1902 by the Zhiyi press 智益書局 in Shanghai. In 1824, Zhang Dunren 張敦仁 published a 3-juan long excerpt of about 3,000 paragraphs, called Tongjian buzheng lüe 通鑑補正略. It was printed by the Dubao Studio 獨抱廬. A reprint was published in 1935 by the Shangwu press 商務印書館. The full text is included in the reprint series Xuxiu siku quanshu 續修四庫全書 and Qiaofanlou congshu 峭帆樓叢書.