# Si

SI is the International System of Units.
SI, Si, or si may also refer to:

## Arts, entertainment, and media
### Literature

* Si (novel), a 2014 novel by Bob Ong
* Sí (Peruvian magazine), a magazine notable for its anti-corruption reporting
* Skeptical Inquirer, an American magazine covering topics on science and skepticism
* Sports Illustrated, an American sports magazine

### Music

* Sí (Julieta Venegas album), released in 2003
* Sì (Andrea Bocelli album), released in 2018
* "Sí" (Martin Jensen song), a 2015 song
* Si (musical note), the seventh note in the traditional fixed do solfège
* Sì (operetta), an operetta by the Italian composer Pietro Mascagni
* "Sì" (Gigliola Cinquetti song), the Italian entry to the Eurovision Song Contest 1974
* Si (Zaz song), 2013
* Sí, a 2013 Spanish album by Malú
* "Sì", a 1985 song released by Italian actress Carmen Russo

### Other uses in arts, entertainment, and media

* Si (film), original title of the 2010 South Korean film Poetry

## Enterprises and organisations
### Computing

* Swiss Informatics Society, a Swiss organization of computer science educators, researchers, and professionals
* The SI, a former name of the American defense contractor Vencore

### Education

* St. Ignatius College Preparatory, a Jesuit high school in San Francisco, California, US
* Silay Institute, a private college in the Philippines

### Government

* Si, a South Korean administrative unit
* Survey of India, an Indian government agency responsible for managing geographical information
* Swedish Institute (Svenska institutet), a Swedish government agency which promotes Sweden abroad

### Politics

* Sarekat Islam, a socio-political organization in Indonesia under Dutch colonial rule
* Catalan Solidarity for Independence, a Catalan political party
* Situationist International, an organization of social revolutionaries
* Socialist International, a worldwide organization of political parties
* Solidarity and Equality, an Argentine political party (Spanish: Solidaridad e Igualdad)

### Transportation

* Blue Islands (IATA airline code, SI)
* Skynet Airlines (IATA airline code SI, ceased operating 2004)
* Spokane International Railroad (reporting mark SI), a former railway in Washington, US

### Other enterprises and organizations

* Samahang Ilokano, a fraternity/sorority based in the Philippines
* SÍ Sørvágur, a Faroese sports association
* Society of Indexers, a professional society based in the UK
* Sports Interactive, a British computer games development company

## People with the name

* Si (surname), a Chinese surname
* Si (given name)

## Places

* Mount Si, a mountain in the U.S. state of Washington
* Province of Siena (postal code and vehicle registration plate code)
* Si County, Anhui, China
* Si River, in China
* Slovenia's ISO 3166-2 code

## Science and technology
### Biology and healthcare

* Smithsonian Institution (SI is its international code)
* Sacroiliac, an anatomical abbreviation for the sacroiliac (joint)
* Self-injury, intentional, direct injuring
* Shock index, a measurement used to determine if a person is suffering shock

### Chemistry

* si, a chemical descriptor; See prochirality
* Silicon, symbol Si, a chemical element
* Disulfur diiodide, empirical formula SI

### Computing and Internet

* .si, the Internet country code top-level domain for Slovenia
* Shift In, an ASCII control character
* SI register, or source index, in X86 computer architecture
* Swarm intelligence, an artificial intelligence technique
* Synthetic intelligence, an alternate term for or a form of artificial intelligence

### Motor vehicles

* Honda Civic Si, an automobile
* Spark-ignition engine, a type of internal combustion engine

### Other uses in science and technology

* Signal integrity, electronic circuit tools and techniques that ensure electrical signals are of sufficient quality
* Sine integral, Si(x)
* Spectral interferometry, attosecond physics technique

## Titles and ranks

* Si, a Maghrebi Arabic variant of Sidi, a title of respect
* Si, a variant of the Thai honorific Sri
* Station inspector, a rank in the Singapore Police Force
* Sub-inspector, a rank in Indian Police forces

## Other uses

* Statutory instrument (UK), abbreviated SI, the principal form in which delegated legislation is made in Great Britain
* Sì (dessert), a Chinese dessert
* Sídhe, Sí, or Sìth, Celtic mythological beings
* si, the Sinhala language ISO 639 alpha-2 code
* Supplemental instruction, an academic support program often used in higher education