PL/I (Programming Language One) is a procedural, imperative language developed by IBM in the 1960s, designed to unify scientific, business, and system programming under a single syntax. It originated from a 1963 committee tasked with extending Fortran, but the group instead created a new language based on ALGOL, initially called NPL and renamed PL/I in 1965. The first compiler was delivered in 1966, and the language was later formalized as an ANSI technical standard (X3.53-1976) in 1976. Its notable features include recursion, structured programming, and versatile data handling (fixed-point, floating-point, complex, character, and bit strings), making it ideal for describing and manipulating complex data formats. Key contributors included Fred Brooks, who ensured the character data type, and Christopher J. Date, who added relational database extensions based on Edgar Codd's work. PL/I has been in continuous use by academic, commercial, and industrial organizations since its introduction and also spurred the development of formal methods like VDM.