动态链接函式库（英语：Dynamic-link library，缩写为DLL）是微软公司在微软视窗操作系统中实现共享函数库概念的一种实作方式。这些函式库函数的扩展名是.DLL、.OCX（包含ActiveX控制的函式库）或者.DRV（旧式的系统驱动进程)。

所谓动态链接，就是把一些经常会共用的代码（静态链接的OBJ程序库）制作成DLL档，当运行档调用到DLL档内的函数时，Windows操作系统才会把DLL档加载内存内，DLL档本身的结构就是可运行档，当程序需求函数才进行链接。透过动态链接方式，内存浪费的情形将可大幅降低。静态链接函式库则是直接链接到运行档。

Dynamic-link library (or DLL) is Microsoft's implementation of the shared library concept in the Microsoft Windows and OS/2 operating systems. These libraries usually have the file extension DLL, OCX (for libraries containing ActiveX controls), or DRV (for legacy system drivers). The file formats for DLLs are the same as for Windows EXE files – that is, Portable Executable (PE) for 32-bit and 64-bit Windows, and New Executable (NE) for 16-bit Windows. As with EXEs, DLLs can contain code, data, and resources, in any combination.