Emperor Wenzong of Tang (809–840), personal name Li Ang, né Li Han (李涵), was an emperor of the Tang dynasty of China. He reigned from 827 to 840. Emperor Wenzong was the second son of Emperor Muzong and younger brother of Emperor Jingzong. A rare occurrence in Chinese history, Emperor Wenzong, along with his elder brother Emperor Jingzong and younger brother Emperor Wuzong, reigned in succession.

Li Han was born in late 809, during the reign of his grandfather Emperor Xianzong. His father, Li You was then the Prince of Sui under Emperor Xianzong, but while Li You was considered, under Confucian principles of succession, to be the proper heir to the throne, because his mother (Li Han's grandmother) Consort Guo, was Emperor Xianzong's wife and crown princess while Emperor Xianzong was crown prince, Li You was not created crown prince for some time; his older brother Li Ning, by Emperor Xianzong's concubine Consort Ji, was. Only after Li Ning's death in 811 was Li You, whose name was then changed to Li Heng, created crown prince in 812. Li Han was Li You's second son, being born four months after his older brother Li Zhan. His mother was Li You's concubine Consort Xiao.

In 820, Emperor Xianzong died, and Li Heng took the throne (as Emperor Muzong). In 821, Emperor Muzong created a large number of his brothers and sons imperial princes, and Li Han was created the Prince of Jiāng. In 824, Emperor Muzong died and was succeeded by Li Zhan (as Emperor Jingzong). Around the new year 827, Emperor Jingzong was assassinated by a group of imperial guards and eunuchs, led by the eunuch Liu Keming (劉克明). Liu initially tried to have Emperor Muzong's younger brother Li Wu the Prince of Jiàng (note different tone) made emperor, but soon, a group of powerful eunuchs—the directors of palace communications Wang Shoucheng and Yang Chenghe (楊承和) and commanders of the Shence Armies Wei Congjian (魏從簡) and Liang Shouqian (梁守謙) counteracted against the conspirators, launching forces to slaughter them. Li Wu was also killed in this event. Wang and the other eunuchs subsequently had Li Han named the new emperor by orders issued in the name of his grandmother Consort Guo (who was then grand empress dowager) (as Emperor Wenzong). His name was changed to Li Ang.

It was said that at the start of Emperor Wenzong's reign, he, having observed the wastefulness that his father Emperor Muzong and brother Emperor Jingzong displayed in their reigns, sought to conserve, govern diligently, and meet with the officials frequently. The people thought that a peaceful time would be coming. However, it was also said that Emperor Wenzong, while humble and willing to open to suggestions, was indecisive, often changing his mind after initially agreeing to the chancellors' suggestions. At one point, the chancellor Wei Chuhou objected and offered to resign, but Emperor Wenzong did not accept his resignation. Meanwhile, Emperor Wenzong honored his mother Consort Xiao as an empress dowager, and continued to honor his grandmother Grand Empress Dowager Guo and Emperor Jingzong's mother Empress Dowager Wang as well, so there were three empresses dowager in the palace. It was said that he served them with filial piety, always offering the best of the tributes to them first.

One of the major moves that Emperor Wenzong had to make, however, dealt with war—as, at the very end of Emperor Jingzong's reign, after the death of Li Quanlüe (李全略) the military governor (Jiedushi) of Henghai Circuit (橫海, headquartered in modern Cangzhou, Hebei), Li Quanlüe's son Li Tongjie seized control of the circuit without imperial sanction, hoping to succeed his father. Initially, the imperial government took no action, and after Emperor Wenzong took the throne, Li Tongjie sent his secretary Cui Congzhang (崔從長) and brothers Li Tongzhi (李同志) and Li Tongsun (李同巽) to the capital Chang'an to pay homage to Emperor Wenzong, hoping that Emperor Wenzong would approve of his succession. In response, Emperor Wenzong commissioned Li Tongjie as the military governor of Yanhai Circuit (兗海, headquartered in modern Jining, Shandong) and transferred a former military governor of Henghai, Wu Chongyin, to Henghai. Li Tongjie decided to resist militarily, and he was supported by the warlord Wang Tingcou, the military governor of neighboring Chengde Circuit (成德, headquartered in modern Shijiazhuang, Hebei). Emperor Wenzong mobilized a number of circuits around Henghai to attack it, but could not immediately achieve success. Not until 829 was Li Tongjie defeated by the imperial general Li You (note different character than Emperor Muzong).

In the aftermath of Li Tongjie's defeat, however, one of the other warlords of the region, Shi Xiancheng the military governor of Weibo Circuit (魏博, headquartered in modern Handan, Hebei), fearing that he would be the imperial forces' next target, offered to surrender his circuit to imperial control. Emperor Wenzong transferred Shi to Hezhong Circuit (河中, headquartered in modern Yuncheng, Shanxi) and commissioned the imperial general Li Ting (李聽) to succeed him. Before Shi could depart Weibo, however, the Weibo soldiers mutinied, killed him, and supported the officer He Jintao as their leader in resisting Li Ting. Subsequently, He Jintao defeated Li Ting, and the imperial government, with its treasury drained by the Henghai campaign, decided not to wage another war, and Emperor Wenzong allowed He Jintao to become the military governor of Weibo.

In late 829, Nanzhao, irritated by incursions by Tang's Xichuan Circuit (西川, headquartered in modern Chengdu, Sichuan) troops, who were forced to resort to raiding Nanzhao's border regions due to the reduction in salaries by Xichuan's military governor, the former chancellor Du Yuanying, made a major attack against Xichuan. The Nanzhao forces advanced all the way to Chengdu, almost capturing it. Nanzhao demanded that Emperor Wenzong take action against Du, and Emperor Wenzong exiled him and subsequently entered into a peace agreement with Nanzhao. Still, Nanzhao forces seized tens of thousands of people from Xichuan and took them to Nanzhao as captives.

830 saw the start of factionalism, later known as the Niu-Li Factional Struggles, within Emperor Wenzong's administration—as, by this point, Wei Chuhou had died, and fellow chancellor Pei Du, in his old age, had taken less of a lead on government decisions (and was eventually sent out of the capital to serve as a military governor). The succeeding chancellors Li Zongmin and Niu Sengru were considered factional figures (of the faction historians later referred to as the Niu Faction, named after Niu), and they, together, ejected allies of their political rival Li Deyu (after whom the Li Faction was later named by historians) from government. (Pei had recommended Li Deyu to be chancellor, but Li Zongmin was said to have triumphed over Li Deyu due to assistance by the eunuchs.) Meanwhile, Emperor Wenzong, tired of the eunuchs' influence over his governance and control of the palace, was secretly planning with the official Song Shenxi on how the eunuchs, particularly Wang Shoucheng, could be disarmed. To further plan this, Emperor Wenzong made Song a chancellor as well. However, when Wang and his strategist Zheng Zhu later heard about the plot in 831, they counteracted by falsely accusing Song of planning to overthrow Emperor Wenzong and replace him with his brother Li Cou the Prince of Zhang. As a result, both Li Cou and Song were exiled.