WordStar is a word processor application for microcomputers. It was published by MicroPro International and originally written for the CP/M-80 operating system, and later written also for MS-DOS and other 16-bit PC OSes. Rob Barnaby was the sole author of the early versions of the program. Starting with WordStar 4.0, the program was built on new code written principally by Peter Mierau. WordStar dominated the market in the early and mid-1980s, succeeding the market leader Electric Pencil.

WordStar was written with as few assumptions as possible about the operating system and machine hardware, allowing it to be easily ported across the many platforms that proliferated in the early 1980s. Because all of these versions had relatively similar commands and controls, users could move between platforms with equal ease. It was already popular when its inclusion with the Osborne 1 portable computer made the program the de facto standard for much of the small computer word-processing market.

As the market became dominated by the IBM PC and later Microsoft Windows, this same portable design made it difficult for the program to add new features, and affected its performance. In spite of its great popularity in the early 1980s, these problems allowed WordPerfect to take WordStar's place as the most widely used word processor from 1985 on.