LSI may mean:
- LSI Corporation, a technology company founded in 1981
- LSI-11, an early large-scale integration computer processor that implemented the DEC PDP-11 instruction set
- "LSI (Love Sex Intelligence)", a single by The Shamen
- Lynch Syndrome International, non-profit organisation supporting those affected by Lynch Syndrome
- Labour and Socialist International, a former socialist international
- Lake Superior and Ishpeming Railroad, a railroad service in Michigan, U.S.
- Landing Ship, Infantry, a type of troopship or post WWII a landing craft
- Langelier Saturation Index, a measure for water's tendency to form scale
- Large Scale Integration, integrated circuits with tens of thousands of transistors
- La Salle Institute, a college preparatory school
- Latent semantic indexing, a technique in natural language processing
- Lear Siegler Inc., a technology company active from 1961-2002
- Lëvizja Socialiste për Integrim, an Albanian political party
- Linear shift-invariant systems, the discrete equivalent of linear time-invariant systems
- Linguistic Survey of India, a survey of the languages of British India directed by G.A. Grierson
- Logical Sensory Introvert, a socionics type
- Long string instrument, a musical instrument
- Lord Steel Industry, a manufacturer of stainless steel tubing and piping
- LSI, the IATA airport code for Sumburgh Airport in Shetland, Scotland