High Quality Content by WIKIPEDIA articles! PL/I ("Programming Language One", PEE-EL-WUN) is a procedural, imperative computer programming language designed for scientific, engineering, business and systems programming applications. It has been used by various academic, commercial and industrial users since it was introduced in the 1960s, and is actively used as of 2010[update]. PL/I's principal domain is data processing; it supports numerical computation, scientific computing, recursion, structured programming, linked data structure handling, character string handling, and bit string handling. The language syntax is English-like and suited for describing complex data formats, with a wide set of functions available to verify and manipulate them.