LSI may refer to:

• Large-scale integration, integrated circuits with tens of thousands of transistors
• Latent semantic indexing, a technique in natural language processing
• LSI-11, an early large-scale integration computer processor that implemented the DEC PDP-11 instruction set
• Langelier saturation index, a measure for water's tendency to form scale
• Linear shift-invariant systems, the discrete equivalent of linear time-invariant systems

• LSI Corporation, a technology company founded in 1981 as LSI Logic Corporation
• Lynch Syndrome International, non-profit organisation supporting those affected by Lynch Syndrome
• Labour and Socialist International, a multinational federation of left wing political parties and trade unions active between 1923 and 1940
• Socialist Movement for Integration (Lëvizja Socialiste për Integrim), a political party in Albania
• Lear Siegler Incorporated, a technology company active from 1961 to 2002
• Lingkaran Survei Indonesia, a survey company in Indonesia

• Lake Superior and Ishpeming Railroad, a railroad service in Michigan, United States
• Sumburgh Airport (IATA airport code) in Shetland, Scotland

• "LSI (Love Sex Intelligence)", a single by The Shamen
• Long-string instrument, a musical instrument

• Landing ship, infantry, a type of troopship or post World War II a landing craft
• La Salle Institute, a college preparatory school
• Linguistic Survey of India, a survey of the languages of British India directed by G.A. Grierson
• Logical Sensory Introvert, a socionics type
• Lighting & Sound International, a trade magazine