EI or Ei may refer to:

Arts and media

• "E.I." (song), a single by Nelly
• E/I, a type of children's television programming shown in the United States
• Ei (album), an album by Maija Vilkkumaa
  • "Ei" (song), its first single
• Eerie, Indiana, an American television series
• Enrique Iglesias, Spanish pop music singer-songwriter
• Exposure index, the film speed rating of photographic film as exposed

Businesses and organizations

• Aer Lingus (IATA code EI), the flag airline of Ireland
• The Earth Institute, a collection of research centers at Columbia University
• Education International, a global union federation of teachers' trade unions
• Elektronska Industrija Niš, electronics enterprise based in Niš, Serbia
• Energy Institute, the main professional organization for the energy industry within the UK
• Engineers Ireland, the professional body for engineers and engineering in Ireland
• Enterprise Ireland, is the Irish government organisation responsible for the development and growth of Irish enterprises in world markets.
• Expeditors International, the global logistics and freight forwarding company based out of Seattle, Washington
• The Electronic Intifada, an online publication covering the Israeli-Palestinian conflict from a Palestinian perspective

Linguistics

• ⟨ei⟩, a digraph found in some Latin alphabets
• The original name of the Greek letter Epsilon
• ɛɪ in the International Phonetic Alphabet (IPA)

Places

• Ei, Kagoshima, a town located in Ibusuki District, Kagoshima, Japan
• Emerald Isle, North Carolina, a town in Carteret County, North Carolina, United States

Science, technology, and mathematics

• Ei (prefix symbol), the prefix abbreviation of the binary unit prefix "exbi"
• Earth Interactions, a scientific journal published by the American Meteorological Society, American Geophysical Union, and Association of American Geographers
• Ei Compendex, an engineering bibliographic database
• Electron ionization, an ionization method in which energetic electrons interact with gas phase atoms or molecules to produce ions
• Electronic ignition, a variety of modern ignition system
• Engineering Index, an article index for engineering journals
• Engineer intern, an intermediary step to becoming a Professional Engineer
• Environmental illness (multiple chemical sensitivity), a chronic medical condition characterized by symptoms that the affected person attributes to exposure to low levels of chemicals
• Ionization energy (E_I), the energy required to remove one electron from one atom to another
• Equine influenza, the disease caused by strains of Influenza A that are enzootic in horse species
• Exponential integral, a special function defined on the complex plane given the symbol Ei

Other uses

• Education Index, a United Nations measure of the level of educational development in a country
• Emotional intelligence, the ability to identify, assess, and control emotions
• Employment insurance, the unemployment benefits system of Canada
• Encyclopaedia of Islam, an encyclopaedia of the academic discipline of Islamic studies
• Enhanced interrogation, a euphemism for torture
• Ex infra, a Latin phrase meaning 'from below'
• Extreme ironing, an extreme sport and a performance art
• Esercito Italiano, Italian language for Italian Army
• Raiden Shogun, real name Raiden Ei, a playable character from Genshin Impact