Tan may refer to:
- Tanbark, or tan, bark of certain species of tree
- Tan (color), pale shade of brown
- Tangent function, or tan, one of the main trigonometric functions
- Tanning, the process of making leather from hides
- Sun tanning, the darkening of skin in response to ultraviolet light
- Sunless tanning, the darkening of skin without ultraviolet light
- Tan (goat pattern), goat color pattern
- Tanfana, or Tan, ancient European goddess
- Tan (surname) (譚), a Chinese surname
- Chen (surname) (陳), a Chinese surname, pronounced "Tan" in Min Nan languages
- Lao Zi, posthumous name "Tan" or "Dān" (聃), philosopher of ancient China
- TAN Books & Publishers, a Catholic publishing company
- OS-tan, an Internet phenomenon on Futaba Channel
- Tan (album), a live album by the Polish rock band Kult
- Tahn, a yoghurt-based drink from the Middle East
- Tan (state), ancient Chinese kingdom situated in eastern Shandong Province
- Leborgne, nickname Tan, a patient of Paul Broca, on whose autopsy he identified Broca's area
"TAN" or "tan" may also be a three-letter abbreviation for:
- Tanzania (IOC and FIFA trigram; the ISO 3166 trigram is TZA)
- Thrust Augmented Nozzle -- an advanced rocket nozzle design.
- Total Acid Number, the measure of a lubricant's or crude oil's acidity
- Transaction authentication number in electronic banking
- Tree augmented naive Bayes, a probabilistic classifier based on applying Bayes' theorem
- Taunton Municipal Airport, IATA airport code TAN, airport in Taunton, Massachusetts
- Tax Deduction Account Number, issued by Indian Income Tax Department for deduction of tax at source.
- Thunderbirds Are Now!, a Detroit-based neo-post-punk band
- Tenth Avenue North, a Contemporary Christian band
- The Anime Network, an all-anime channel
- This Aint News, a social news website with a firm stance on preserving Freedom of speech
- Tiny area network, a local area network with 2–3 nodes connection, usually implemented for shared files, folders and printers in a home or small office environment
- Total amoniacal Nitrogen, Nitrogen content in form of ammonium