Emperor Taizong (r. 626-649) receives Ludongzan; ambassador of Tibet; at his court; painted in 641 CE by Yan Liben (600-673); detail from scroll painting.

Emperor Taizong of Tang (January 23; 599 - July 10; 649); personal name Li Shimin; was the second emperor of the Tang Dynasty of China; ruling from 626 to 649. He is ceremonially regarded as a co-founder of the dynasty along with Emperor Gaozu. He is typically considered one of the greatest; if not the greatest; emperors in Chinese history. Throughout the rest of Chinese history; Emperor Taizong's reign was regarded as the exemplary model against which all other emperors were measured; and his era was considered a golden age of Chinese history and required study for future crown princes.

During his reign; Tang China flourished economically and militarily. For more than a century after his death; Tang China enjoyed peace and prosperity. During Taizong's reign; Tang was the largest and the strongest nation in the world. It covered most of the territory of present-day China; Vietnam; Mongolia and much of Central Asia as far as eastern Kazakhstan. It laid the foundation for Xuanzong's reign; which is considered Tang China's greatest era.