A word processor is an electronic device or a computer application software that performs word processing: the composition, editing, formatting and sometimes printing of any sort of written material. Word processing can also refer to advanced shorthand techniques, sometimes used in specialized contexts with a specially modified typewriter. The term was coined at IBM's Böblingen, West Germany Laboratory in the 1960s. Typical features of a word processor include font application, spell checking, grammar checking, a built-in thesaurus, automatic text correction, Web integration and HTML exporting, among others.

The word processor emerged as a stand-alone office machine in the 1970s and 1980s, combining the keyboard text-entry and printing functions of an electric typewriter with a dedicated computer processor for the editing of text. Although features and designs varied among manufacturers and models, and new features were added as technology advanced, word processors typically featured a monochrome display and the ability to save documents on memory cards or diskettes. Later models introduced innovations such as spell-checking programs, improved formatting options, and dot-matrix printing. As the more versatile combination of personal computers and printers became commonplace, and computer software applications for word processing became popular, most business machine companies stopped manufacturing word processor machines. As of 2009 there were only two U.S. companies, Classic and AlphaSmart, which still made them. Many older machines, however, remain in use. Since 2009, Sentinel has offered a machine described as a "word processor", but it is more accurately a highly specialised microcomputer used for accounting and publishing.

Word processors are descended from early text formatting tools (sometimes called "text justification" tools, from their only real capability). Word processing was one of the earliest applications for the personal computer in office productivity.

Although early word processors used tag-based markup for document formatting, most modern word processors take advantage of a graphical user interface providing some form of what-you-see-is-what-you-get editing. Most are powerful systems consisting of one or more programs that can produce any arbitrary combination of s, graphics and text, the latter handled with type-setting capability.

Microsoft Word is the most widely used word processing software. Microsoft estimates that over 500,000,000 people use the Microsoft Office suite, which includes Word. Many other word processing applications exist, including WordPerfect (which dominated the market from the mid-1980s to early-1990s on computers running Microsoft's MS-DOS operating system) and open source applications OpenOffice.org Writer, LibreOffice Writer, AbiWord, KWord, and LyX. Web-based word processors, such as Office Web Apps or Google Docs, are a relatively new category.