在计算机科学中，预处理器是进程中处理输入数据，产生能用来输入到其他进程的数据的进程。输出被称为输入数据预处理过的形式，常用在之后的进程比如编译器中。所作处理的数量和种类依赖于预处理器的类型，一些预处理器只能够执行相对简单的文本替换和巨集展开，而另一些则有着完全成熟的编程语言的能力。

一个来自计算机编程的常见的例子是在进行下一步编译之前，对源代码执行处理。在一些计算机语言（例如：C语言）中有一个叫做预处理的翻译阶段。

In computer science, a preprocessor is a program that processes its input data to produce output that is used as input to another program. The output is said to be a preprocessed form of the input data, which is often used by some subsequent programs like compilers. The amount and kind of processing done depends on the nature of the preprocessor; some preprocessors are only capable of performing relatively simple textual substitutions and macro expansions, while others have the power of full-fledged programming languages.