Eta (Η or η) is the seventh letter of the Greek alphabet.

Eta or ETA may also refer to:

• Eta (given name)
• Eta, a derogatory term for the Burakumin in the Japanese feudal era
• ETA, an Elvis Tribute Artist

• Eta (glider), a German glider
• CNA Eta, an Italian aircraft

• Eta, a snack food brand owned by Griffin's Foods
• Empresa de Transporte Aéreo, a defunct Brazilian Airline
• Environmental Transport Association, a British roadside assistance company
• ETA SA, a Swiss watchmaking company
• ETA Star Group, a Dubai-based investment company
• ETA Systems, a defunct American computer manufacturer

• Engineering & Technologies Academy, in San Antonio, Texas, United States
• Ethiopian Teachers' Association, a trade union
• Evangelical Theological Academy, in Zwijndrecht, Netherlands
• Evangelical Theological Association, a former teaching institute in Melbourne, Australia

• ETA (separatist group) (Basque: Euskadi Ta Askatasuna), a Basque armed separatist group
• Electronic Travel Authorization or Electronic Travel Authority, an alternative to a travel visa required by many countries for entry
• Employment and Training Administration, of the United States Department of Labor
• European Technical Assessment of the European Organisation for Technical Approvals

• Dedekind eta function
• Dirichlet eta function
• Eta conversion
• Eta invariant
• Weierstrass eta function
• The small letter eta is used as 't Hooft symbol

• Eicosatetraenoic acid
• Eta meson
• Ethanolamine
• Event tree analysis
• Exfoliatin
• Hapticity
• Pseudorapidity
• Reproduction factor, in the nuclear engineering four factor formula
• Viscosity
• Entropy as defined in Boltzmann's H-theorem
• SARS-CoV-2 Eta variant, one of the variants of SARS-CoV-2, the virus that causes COVID-19

• "E.T.A.", a song by Damon & Naomi from More Sad Hits, 1992
• "E.T.A.", a song by Justin Bieber from Changes, 2020
• "ETA", a song by Dr. Dre, Snoop Dogg, Busta Rhymes and Anderson .Paak from GTA Online: The Contract, 2022
• "ETA" (song), a song by NewJeans from Get Up, 2023

• Estimated time of arrival
• Estimated time of availability, announcement time of re-availability of down systems (servers, websites, etc.)
• England Touch Association, the national governing body for touch rugby within England
• Hurricane Eta, a Category 4 hurricane that occurred in the 2020 Atlantic hurricane season
• 'eta, a letter or glottal stop in the Tahitian languages
• Electronics Technicians Association, a professional association
• Landolphia owariensis, a vine native to Africa and sometimes known as eta

• Eta function (disambiguation)
• Eta Island (disambiguation)