Flex may refer to:

• Flexible electrical cable

In computing

• Adobe Flex, technologies for developing rich internet applications
• Flex, a family of automatic test equipment produced by Teradyne
• Flex lexical analyser, a free software alternative to Lex
• Flex machine, multiple systems
• FLEX (operating system), a single-tasking operating system for the Motorola 6800
• FLEX (protocol), a communication protocol for pagers

In modern culture

• Nigga, Félix Danilo Gómez, Panamanian reggaeton singer, alternatively named "Flex"
• Flex Alexander, Mark Akexabder Knox (b. 1970), an American actor and comedian
• Flex (club), a nightclub in Vienna
• Flex (comics), a fictional superhero
• FLEX (magazine), an American bodybuilding magazine
• Flex (Pitch Black EP)
• Funkmaster Flex, Aston George Taylo Jr (b. 1968), an American hip hop DJ

In science and technology

• Femtosecond Lenticule EXtraction, a form of refractive eye surgery
• Flex-Elektrowerkzeuge, a German producer of power tools
• Flex-fuel, a Flexible-fuel vehicle
• FLEX mission, a potential satellite launch mission by the European Space Agency
• Flextronics (NASDAQ symbo: FLEX), a contract electronics maker in Singapore
• Ford Flex, a full sized people mover vehicle
• Frequency Level Expander, a Pioneer Corporation tape enhancement feature

In other uses

• Flexible spending account, a tax-advantaged savings account
• Flexion, in anatomy, a position made possible by the joint angle decreasing