EM, Em or em may refer to:

• Em, the E minor musical scale
• Em, the E minor chord
• Electronic music, music that employs electronic musical instruments and electronic music technology in its production
• Encyclopedia Metallum, an online metal music database
• Eminem, American rapper

• Em (comic strip), a comic strip by Maria Smedstad

• Em (restaurant), a restaurant in Mexico City
• Aero Benin (IATA code), a defunct airline
• Empire Airlines (IATA code), a charter and cargo airline based in Idaho, US
• Erasmus Mundus, an international student-exchange program
• Estado de Minas, a Brazilian newspaper
• European Movement, an international lobbying association
• ExxonMobil, a large oil company formed from the merger of Exxon and Mobil in 1999
• La République En Marche! (sometimes shortened to "En Marche!"), a major French political party

• Emerging markets, nations undergoing rapid industrialization

• M, a letter of the modern Latin alphabet, in English and other languages
• Em (Cyrillic) (М / м), a letter of the Cyrillic alphabet
• Em (digraph), a digraph in Portuguese
• Em, the third-person singular oblique Spivak pronoun

• em (typography), a unit of measurement
• em dash, a dash that is one em wide
• em space or mutton, a space that is one em wide

• Emergency management, a discipline that studies dealing with and avoiding risks
• Energy management, planning and operation of energy production and energy consumption units
• Environmental management, the management of the interaction of human societies with the environment

• El Monte, California, a city in the United States
• El Monte, Chile, a city in Chile

• Extracellular matrix, the connective tissue supporting cells in multicellular organisms
• Membrane potential (E_m), of a cell

• <em>...</em>, emphasis HTML element
• End of medium, ISO C0 control code ^Y
• Empirical modelling
• em (typography), a unit of measurement in Web design
• eM Client E-Mail client
• A whole brain emulation, see also brain emulation, a hypothetical future life extension technology. Ems were coined by Robin Hanson.

• Effective microorganisms, a series of commercial products advertised to improve soil and plant growth

• Emergency medicine, a medical specialty dealing with acute illnesses and injuries that require immediate attention
• Erythema multiforme, a skin condition that usually follows an antecedent infection or drug exposure
• Erythromelalgia, a disorder that typically affects the skin of the feet and/or hands, causing redness, heat and pain
• Extensive metabolizer, a term used in pharmacogenomics to refer to individuals with normal metabolic activity

• Exametre or exameter (Em), an SI unit of length equal to 10¹⁸ metres
• Electromagnetic spectrum, the range of all possible frequencies of electromagnetic radiation
• Electromigration, the transport of conducting solid material caused by electric current through it
• Electromagnetism, one of the fundamental physical forces
• Electromechanics, combines electrical engineering and mechanical engineering

• Nikon EM, an SLR camera made by the Nikon Corporation in the late 1970s
• Early Minoan, an archaeological period
• Electron microscope, a type of microscope that uses electrons to "illuminate" a specimen and create an enlarged image
• Electron multiplier, a vacuum-tube structure that multiplies incident charges by means of secondary emission
• Electronic monitoring, a form of surveillance used in criminal justice
• Atlantic Equatorial mode, a climate pattern of the Atlantic Ocean
• Expectation–maximization algorithm, an algorithm for finding maximum likelihood estimates of parameters in probabilistic models

• Em Beihold (born 1999), American singer-songwriter
• Em Bryant (born 1938), American professional basketball player
• Em Cooper, British filmmaker and animator
• Em Lindbeck (1934–2008), American professional baseball player
• Em Rossi (born 1998), American singer-songwriter
• Em Rusciano, Australian entertainer
• Em Prasad Sharma (born 1975), Indian politician
• Em Stone (born 1978), American comic book illustrator

• Electrician's mate, an occupational rating in the U.S. Navy and U.S. Coast Guard
• David Em (born 1952), an American computer art pioneer
• EM gauge, a scale used in model railways
• EM TV, a television channel in Papua New Guinea
• Etymologicum Magnum, in the bibliography of the largest Byzantine lexicon