Crimson Editor is an open-source text editor. It is typically used as a source code editor, and HTML editor, for Microsoft Windows.

Crimson Editor features Windows shell integration, tabbed document interface, syntax highlighting, multiple undo/redo, column mode editing, bracket matching, auto-indentation, spell checking, direct editing of text files in FTP and the integration with compilers. Unicode (although only for the characters within the default character set of Windows) and various newlines are supported. Crimson Editor also supports the use of macros. The built-in calculator can evaluate simple expressions. Basic mathematics functions, and date functions are also available.

Crimson Editor as an open source project now being maintained and modified by the members of the Emerald Editor community.