POSIX线程（英语：POSIX Threads，常被缩写为Pthreads）是POSIX的线程标准，定义了创建和操纵线程的一套API。

实现POSIX 线程标准的库常被称作Pthreads，一般用于Unix-like POSIX 系统，如Linux、 Solaris。但是Microsoft Windows上的实现也存在，例如直接使用Windows API实现的第三方库pthreads-w32；而利用Windows的SFU/SUA子系统，则可以使用微软提供的一部分原生POSIX API。

POSIX Threads, usually referred to as Pthreads, is an execution model that exists independently from a language, as well as a parallel execution model. It allows a program to control multiple different flows of work that overlap in time. Each flow of work is referred to as a thread, and creation and control over these flows is achieved by making calls to the POSIX Threads API. API are used for thread creation and synchronization. POSIX Threads is an API defined by the standard POSIX.1c, Threads extensions (IEEE Std 1003.1c-1995).