SAI may stand for:

• The New York Stock Exchange (NYSE) Symbol for Science Applications International Corporation
• SAI (software) a graphics painting program for Microsoft Windows
• Sailfish, two species of fish in the genus Istiophorus
• Scouting Ireland S.A.I., an Irish Scout Association which existed from 1908 to 2004
• Senior Army Instructor, in US Army ROTC
• Serving area interface, or Service Area Interface, an outdoor telecommunications cabinet
• Shaukat Agriculture Industry, an Agriculture Industry, Bhawana, Pakistan
• Silent Aircraft Initiative, a project of the Cambridge-MIT Institute (CMI)
• simulated artificial intelligence
• sistema de alimentacion ininterrumpida (Spanish): uninterruptible power supply)
• Skandinavisk Aero Industri, a former Danish aeroplane manufacturer
• Sigma Alpha Iota, women's music fraternity
• Social Accountability International
• Società Aeronautica Italiana, an Italian aircraft manufacturer
• Societate American pro Interlingua, a North American interlingua organization
• Society of American Indians, an organization of prominent Native Americans active 1911 to 1923
• Society of Architectural Illustration, an organization founded by Eric Monk in 1975
• Software Architects, Inc., a North American computer software company
• Solar America Initiative
• South African Infantry, South African ground troops in World War I
• South Asia Institute
• Sports Authority of India, a body set up by the Government of India
• Stan Ackermans Institute, Institution for technology in the Dutch city of Eindhoven
• Steering Axis Inclination, a secondary wheel alignment measurement
• Sternberg Astronomical Institute, a research institution in Moscow, Russia, a division of Moscow State University
• Strong AI, artificial intelligence that matches or exceeds human intelligence
• Super Adventure Island, a side-scrolling platform game by Hudson Soft
• Supersonic Aerospace International, is a company designing a private supersonic jet
• Supreme audit institutions (Government Audit bodies)
• Sweet Adelines International, International Organization of Women Barbershop Singers

Sai or SAI may refer to:

• self-accrediting institution, a three-letter acronym in use in higher education in Australia to describe universities and other SAIs

Cài (Simplified and Traditional Chinese: ) is a Chinese surname that derives from the name of the ancient Cai state. It is regionally more common in China's Fujian Province and in countries settled by ethnic Chinese from that province than in China as a whole. The surname is the 34th most common surname in China, but the 9th most common in Taiwan, where it is usually romanized as Tsai, and the 8th most common in Singapore, where it is usually romanized as Chua. It is also a common name in Hong Kong where it is romanized as Choy, Choi or Tsoi and in Malaysia as Chua.

Saï is a large island in the Nile River in Nubia between the second and third cataracts. It is 12 km long and 5.5 km wide. Saï was intermittently occupied by the Egyptians during the New Kingdom.

Valea Vinului (, Hungarian pronunciation: ) is a commune of 2,334 inhabitants situated in Satu Mare County, Romania. It is composed of four villages: Marius (Mogyorós), Rosiori (Szamosveresmart), Sâi (Szinfalu) and Valea Vinului.