Dai may refer to:

• Dai (given name), a Welsh or Japanese masculine given name
• Dai (surname) (戴), a Chinese surname
• Bảo Đại (保大), Emperor of Vietnam from 1926 to 1945

• Dai Commandery, a commandery of the state of Zhao and in early imperial China
• Dai County, in Xinzhou, Shanxi, China
• Dai (Eighteen Kingdoms), a short-lived state during the Eighteen Kingdoms period in Chinese history
• Dai (Han dynasty), a realm and title during the Han dynasty
• Dai (Sixteen Kingdoms), a Xianbei-led dynastic state during the Sixteen Kingdoms era of Chinese history
• Dai (Spring and Autumn period), a state during the Spring and Autumn period in Chinese history
• Dai (Warring States period), a short-lived state during the Warring States period in Chinese history

• Da'i al-Mutlaq, or Da'i, a type of religious leader in Islam
• Da'i, person engaging in Dawah, the act of inviting people to Islam
• Dai language (disambiguation)
• Dai people, an ethnic minority of China
• Dai (Yindu), or Daai Chin, an ethnic tribe of Chin, Myanmar

• Dai (cryptocurrency), a cryptocurrency-backed stablecoin
• DAI Personal Computer, an early home computer from Belgium
• Mercedes-Benz Group's former Frankfurt Stock Exchange stock symbol
• De Administrando Imperio, work written by the 10th-century Byzantine Emperor Constantine VII
• Deutsches Archäologisches Institut, or German Archaeological Institute, an archaeological institute operated by the German ministry of foreign affairs
• DAI Global, an international development firm
• Diamond Aircraft Industries, an aircraft manufacturer
• Diffuse axonal injury, a type of traumatic brain injury
• Digital Author Identifier, a unique number for an author in the Dutch research system
• Direct audio input, a port used in hearing aids and hearing instruments
• Distributed artificial intelligence, a subfield of artificial intelligence
• Do As Infinity, a Japanese band
• Dragon Age: Inquisition, a video game by BioWare
• Dynamic ARP Inspection, a security protocol