The integral symbol:
is used to denote integrals and antiderivatives in mathematics. The notation was introduced by the German mathematician Gottfried Wilhelm Leibniz towards the end of the 17th century. The symbol was based on the ſ (long s) character, and was chosen because Leibniz thought of the integral as an infinite sum of infinitesimal summands. See long s for more details on the history of ſ.
Typography in Unicode and LaTeX 
Fundamental symbol 
The original IBM PC code page 437 character set included a couple of characters ⌠ and ⌡ (codes 244 and 245, respectively) to build the integral symbol. These were deprecated in subsequent MS-DOS code pages, but they still remain in Unicode (U+2320 and U+2321, respectively) for compatibility.
Extensions of the symbol 
Meaning Unicode LaTeX Double integral ∬ U+222C
Triple integral ∭ U+222D
Contour integral ∮ U+222E
Clockwise integral ∱ U+2231 Anticlockwise integral ⨑ U+2A11 Clockwise contour integral ∲ U+2232
Anticlockwise contour integral ∳ U+2233
Closed surface integral ∯ U+222F
Closed volume integral ∰ U+2230
Typography in other languages 
In other languages, the shape of the integral symbol differs slightly from the shape commonly seen in English-language textbooks. While the English integral symbol leans to the right, the German symbol (used throughout Central Europe) is upright, and the Russian variant leans to the left.
See also 
- Stewart, James (2003). "Integrals". Single Variable Calculus: Early Transcendentals (5th edition ed.). Belmont, CA: Brooks/Cole. p. 381. ISBN 0-534-39330-6.
- Zaitcev, V.; Janishewsky, A.; Berdnikov, A. (1999), "Russian Typographical Traditions in Mathematical Literature", EuroTeX'99 Proceedings