并发计算（英语：Concurrent computing，或译为并行处理、共时计算），是一种程序计算的形式，在系统中，至少有两个以上的计算在同时运作，计算结果可能同时发生。用来实作并行系统（Concurrent system）的编程语言与各种算法，统称为并行计算。

并行程序通常被设计为交互式的运算过程，因为它的运算过程是不确定的，在设计上的难度较高。设计并行程序最大的挑战，在于确保不同运算运行步骤间的交互或是通信，能以正确的顺序进行，同时，也要确保在不同运行步骤间共享的资源，能够正确被访问。在这个领域的先驱人物有艾兹赫尔·戴克斯特拉、东尼·霍尔与泊·派克·汉森等人。

Concurrent computing is a form of computing in which several computations are executing during overlapping time periods—concurrently—instead of sequentially (one completing before the next starts). This is a property of a system—this may be an individual program, a computer, or a network—and there is a separate execution point or "thread of control" for each computation ("process"). A concurrent system is one where a computation can advance without waiting for all other computations to complete; where more than one computation can advance at the same time.