Paint.Net is a free and open source photo editing program for Microsoft Windows. It was originally created by Rick Brewster as a free replacement for Microsoft Paint, which comes bundled with Windows. It has since been maintained by a team of developers at dotPDN LLC. Paint.Net is notable for its wide array of features, ease of use, and active online community.

Paint.Net is a raster graphics editor, which means that it can edit images on a pixel-by-pixel basis. It supports various layers of transparency and allows for non-destructive editing, meaning that the original image file is never modified. Paint.Net also supports plugins, which can add new features or extend the existing ones.