在计算机科学中，子程序（英语：Subroutine, procedure, function, routine, method, subprogram, callable unit），是一个大型程序中的某部份代码，由一个或多个语句块组成。它负责完成某项特定工作，而且相较于其他代码，具备相对的独立性。

一般会有输入参数并有传回值，提供对过程的封装和细节的隐藏。这些代码通常被集成为软件库。

函数在面向过程的语言中已经出现。是结构（Struct）和类别（Class）的前身。本身就是对具有相关性语句的归类和对某过程的抽象。

In computer programming, a subroutine is a sequence of program instructions that perform a specific task, packaged as a unit. This unit can then be used in programs wherever that particular task should be performed. Subprograms may be defined within programs, or separately in libraries that can be used by multiple programs. In different programming languages, a subroutine may be called a procedure, a function, a routine, a method, or a subprogram. The generic term callable unit is sometimes used.