Sigma ( or , word-final lowercase ) is the 18th letter of the Greek alphabet.

Sigma may also refer to:

Companies and organizations Sigma (analytics company), an American analytics company Sigma AB, a Swedish IT consultancy company Sigma Alimentos, multinational food processing and distribution company Sigma Corporation, a Japanese camera and lens manufacturer Sigma Designs, Inc., a US semiconductor manufacturer Sigma Guitars, a guitar manufacturing brand Sigma Healthcare, an Australian pharmaceutical company Sigma Motor Corporation, a defunct South African motor vehicle assembler and manufacturer Sigma Motors, a Pakistani assembler of Land Rovers Sigma Sigma Sigma (Tri-Sigma), an American women's sorority centered on education & scholarship Sigma Sport, a German manufacturer of electronic sports equipment SIGMA (Support for Improvement in Governance and Management), a joint initiative of the OECD and the European Union Sigma TV, a television channel in Cyprus Sigma (operations research), a company founded in the UK in 1961 SIGMA (verification service), Nielsen Media Research's tracking system for videos Sigma-Aldrich, an American chemical company Telkomsigma or Sigma Cipta Caraka, an Indonesian IT company

Films and television Sigma (film), a 2026 Indian film Ood Sigma, a fictional character from the Doctor Who series Space City Sigma, a 1980s Indian science fiction TV series Sigma, a fictional character from the anime Tweeny Witches Sigma Society, a fictional Mensa-type club, appearing in the third episode of Columbo sixth season Sigma, a fictional character from the Bungo Stray Dogs manga and anime series

Mathematics Summation operator forming a series in mathematics Σ Standard deviation in statistics σ Divisor function in number theory σ Sigma-algebra (σ-algebra, σ-field) in set theory A busy beaver function in computability theory Σ or , sets in the analytical hierarchy , a set in the polynomial hierarchy Harish-Chandra's σ function Weierstrass sigma function Sigma additivity

Music Sigma (album) Sigma (DJs), a British drum and bass duo Universal Sigma, a Japanese record label under Universal Music Japan Sigma Boy, a 2024 single by Betsy and Maria Yankovskaya

Places Sigma, Capiz, a municipality in the Philippines Sigma, Lee County, Virginia, an unincorporated community in the United States Sığma, Sarayköy, a neighbourhood of the municipality and district of Sarayköy, Denizli Province, Turkey

Products GM Sigma platform, an automobile platform Mitsubishi Sigma, a model name used for various automobiles produced by Mitsubishi Chrysler Sigma, a version of the Mitsubishi Galant sold in Australia Ferrari Sigma, also known as the Pininfarina Sigma, a Formula 1 show car Ford Sigma engine, a series of straight four engines SDS Sigma series of computers from Scientific Data Systems Sigma (sailplane), an experimental glider developed in Britain from 1966 SIGMA 155, a 155mm self-propelled howitzer Six Sigma quality management program Smith & Wesson Sigma, a firearm

Science σ, sigma bond in chemistry σ, sigma factor of RNA polymerase in biology σ, Stefan–Boltzmann constant of radiation in physics σ, stress (mechanics), the force per unit area applied by internal forces of a material σ, the electronic substituent constant for activation of substituted arenes in the Hammett equation σ, a measure of a material's electrical conductivity ability Cross section σ in physics Pauli matrices in quantum physics Sigma baryon in particle physics Sigma receptor, a neural receptor Surface charge density in classical electromagnetism Sigma, a Greek letter used in Bayer designations for naming stars, in astronomy. Notable examples include: Sigma Canis Majoris Sigma Draconis Sigma Octantis Sigma Orionis

Sport Sigma FC, a Canadian soccer team SK Sigma Olomouc, a Czech association football team Histor–Sigma, a Belgian professional cycling team known as Sigma in 1986

Video games Sigma (Mega Man X), the main antagonist of the Mega Man X series Sigma (Overwatch), a hero from Overwatch Ninja Gaiden Sigma, a video game Sigma, a character in the BioShock 2 video game universe Sigma Harmonics, a video game Sigma Klim, a major character and protagonist in the Zero Escape video game series Sigma, a team on the Dota 2 online video game

Other Sigma (couch), used in ancient Roman banquets Sigma class corvette, a naval ship Sigma male, a slang term for masculine men

See also Sygma (disambiguation) M–sigma relation