Guifeng Zongmi (Chinese: 圭峰宗密; pinyin: Guīfēng Zōngmì; Japanese pronunciation: Keihō Shūmitsu) (780–1 February 841) was a Tang dynasty Chinese Buddhist monk and scholar who is considered a patriarch of both the Huayan school and Chan Buddhism. Zongmi wrote a number of works on several Mahayana Sutras, Chan and Huayan, and he also discussed Taoism and Confucianism. His works are a major source for studying the various Chan schools of the Tang.

Zongmi was deeply interested in both the practical and doctrinal aspects of Mahayana Buddhism, especially the teachings of the Sutra of Perfect Enlightenment and the Mahayana Awakening of Faith. Zongmi's work is concerned with harmonizing the various Chan teachings (especially the doctrines of sudden awakening and original enlightenment) with other Chinese Buddhist traditions, especially Huayan, though he also drew on the work of Tiantai Zhiyi in his ritual works. His philosophy attempts to create a comprehensive worldview that includes and sublimates all Buddhist and non-buddhist teachings of his time into a single harmonious spiritual vision.

Zongmi was born in 780 into the powerful and influential He (Chinese: 何) family in what is now central Sichuan. In his early years, he studied the Chinese classics, hoping for a career in the provincial government. When he was seventeen or eighteen, Zongmi lost his father and took up Buddhist studies. In an 811 letter to Chengguan, he wrote that for three years he "gave up eating meat, examined [Buddhist] scriptures and treatises, became familiar with the virtues of meditation and sought out the acquaintance of noted monks."

At the age of twenty-two, he returned to the Confucian classics and deepened his understanding, studying at the Yixueyuan (義學院) Confucian Academy in Suizhou. His later writings reveal a detailed familiarity with the Analects, the Classic of Filial Piety, and the Book of Rites, as well as historical texts and Daoist classics such as the works of Laozi. He eventually converted to Buddhism, but Zongmi's Confucian moral values never left him and he spent much of his career attempting to integrate Confucian ethics with Buddhism.

At the age of twenty-four, Zongmi met the Chan master Suizhou Daoyuan (Chinese: 遂州道圓; pinyin: Suìzhōu Dàoyuán) and trained in Chan for two or three years. He received Daoyuan's seal in 807, the year he was fully ordained as a Buddhist monk. Daoyuan was part of a southern Chan tradition called the Jingzhong school, which was based in Chengdu, Sichuan. This lineage goes back to the Korean prince and Chan master Kim Hwasang (c. 684–762, also known as Jingzhong Wuxiang, 浄衆無相 ), and to his student Shenhui (not to be confused with the earlier Heze Shenhui). According to Broughton, Daoyuan's teacher, Yizhou Nanyin, the abbot of Shengshou Monastery, likely trained with Heze Shenhui and this other Shenhui of Sichuan.

In his autobiographical summary, Zongmi recounts how after a sutra chanting service, he encountered a copy of the Sutra of Perfect Enlightenment. According to Gregory, "after only reading two or three pages, he had an awakening, an experience whose intensity so overwhelmed him that he found himself spontaneously dancing for joy." Zongmi would later write: "at one word [from Daoyuan] my mind-ground opened thoroughly, and with one scroll [of the Scripture of Perfect Enlightenment] its meaning was as clear and bright as the heavens."

Zongmi's sudden awakening during this period had a profound impact upon his subsequent scholarly career. He spent the next several years studying the Sutra of Perfect Enlightenment and its commentaries extensively. He propounded the necessity of scriptural studies in Chan, and was highly critical of what he saw as the antinomianism of the Hongzhou lineage derived from Mazu Daoyi (709–788), which practiced "entrusting oneself to act freely according to the nature of one's feelings".

In 810, at the age of thirty, Zongmi met Lingfeng (Chinese: 靈峯), a disciple of the preeminent Buddhist scholar and Huayan exegete Chengguan (Chinese: 澄觀, 738–839). Lingfeng gave Zongmi a copy of Chengguan's commentary and sub-commentary on the Avatamsaka Sutra. The two texts were to have a profound impact on Zongmi. He studied these texts and the sūtra with great intensity, declaring later that due to his assiduous efforts, finally "all remaining doubts were completely washed away." In 812 Zongmi travelled to the western capital, Chang'an, where he spent two years studying with Chengguan, who was not only the undisputed authority on Huayan, but was also highly knowledgeable in Chan, Tiantai, the vinaya and East Asian Mādhyamaka.