Confucians and Daoists, Wansong Xingxiu wrote in the first chapter of his best-known book, trace all things back to one primal breath, qi; Buddhists trace them to the one mind. Then he takes a side. He cites Zongmi, a ninth-century scholar-monk, for the view that the primal breath is itself something the mind produces. The verse he is explaining at that moment is not his own, and neither is most of what the book contains. Wansong built his reputation on other men's words: a remembered exchange between earlier masters, a poem on it by Hongzhi Zhengjue (1091–1157), the great master of his own Caodong line of Chan, and around them a commentary that reaches into the Confucian classics, the histories and the Daoist books. His claim is that the old cases of Chan do not stand against the learning of China; read with all of it, they still point past it, to the mind that every teaching rests on.
He lived his whole life under rulers who were not Chinese. Born in 1166 into the Cai family of Hezhong, in today's Shanxi, he grew up in a north China ruled by the Jurchen Jin dynasty. At fifteen he became a monk at Xingzhou, studied under Xueyan Huiman, a Caodong master at Cizhou, and returned to a hall called Wansong, "ten thousand pines", which gave him his name. In 1193 Emperor Zhangzong of Jin called him to court to expound the teaching and gave him a brocade robe. From 1197 he lived at the Bao'en monastery west of the capital, Zhongdu, today's Beijing, in a hermitage named Congrong, "serenity".
The Mongols took Zhongdu in 1215, and the Jin court fled south to Kaifeng. Wansong stayed. That year Yelü Chucai, a Khitan official of the Jin who had lived through the siege, became his pupil and studied with him for three years, until Genghis Khan summoned him in 1218. Wansong had once lectured on Hongzhi's hundred verses on old cases, but the work had lapsed in the wars. At the end of 1222 a letter from Yelü reached him insisting that he finish it, and in 1223 he sent the commentary to Almaliq in Central Asia, where Yelü was then in Genghis Khan's service. His covering letter says that his eyes were failing, that he mostly dictated while his disciples wrote, and that he had followed the Blue Cliff Record, Yuanwu Keqin's commentary on the verses of Xuedou Chongxian, in giving every case an introduction. In the same letter he says the book transmits rather than invents, borrowing the phrase Confucius used of himself.
The Book of Serenity is the result. It explains one of Hongzhi's verses through the Tang essayist Han Yu's mock biography of a writing brush and another through the Daoist book Liezi's story of a sheep lost where the road forks. He wrote a second commentary on Hongzhi's prose remarks on old cases, became abbot of the Wanshou monastery in 1230, and died in 1246. His disciples built a brick pagoda for his remains in what is now central Beijing; it was enclosed in a larger pagoda in 1753 and found intact inside it in 1986.
The book's reception came later and further east. In Japan the Sōtō school of Zen, heir to the Caodong line, came to hold the Book of Serenity in the place the Rinzai school gives the Blue Cliff Record, and Thomas Cleary's complete English translation appeared in 1990.