Zai may refer to:
- Democratic Republic of the Congo, formerly Zaire, ongoing UNDP code ZAI
- Zaï, an off season farming technique to collect water and nutrients from compost, to restore degraded drylands and increase soil fertility
- Zai (surname) (宰), a Chinese surname
- Zai (suffix), suffix denoting a member of certain Pashtun tribes
- Zai, Palghar, a village in Maharashtra, India
- Zväz autorov a interprétov populárnej hudby (Union of Authors and Performers, ZAI), a presenter of the ZAI Awards
- Zaire, a former state in Africa
- Zayin, a letter of many Semitic abjads
- Isthmus Zapotec (ISO 639-3: zai), a Zapotecan language of Mexico