PEI or Pei may refer to:
- Places
- Prince Edward Island, a province of Canada
- Pei, Tibet, a town in Tibet
- Pei County (沛县), a county in Xuzhou, Jiangsu, China
- People
- I. M. Pei (貝聿銘) (born 1917), a Chinese-American architect
- Mario Pei (1901–1978), an Italian-American linguist and polyglot
- Pei Wenzhong (裴文中) (1904–1982), a Chinese anthropologist
- Yan Pei-Ming (born 1960), a Chinese born painter
- Polymers
- Polyethylenimine, a type of water-soluble polymer
- Polyetherimide, an amorphous, amber-to-transparent thermoplastic with characteristics similar to the related plastic PEEK
- Other
- Pei (פ) a letter in the Hebrew alphabet
- Shar Pei, a breed of dog whose distinctive feature is deep wrinkles
- Pei (surname) (裴), a Chinese surname
- PEI, Patient Episode Initiation, a chargeable service item under the Medicare (Australia) benefits scheme
- Private Equity International, a financial magazine