libvips is a LGPL licensed (open source and free for commercial use), portable, horizontally-threaded, demand-driven, 2D image processing library with its origins in imaging research projects. Compared to similar libraries, libvips runs quickly and uses little memory. It supports numeric formats from 8-bit integer to 128-bit complex, any number of color separation bands, most popular image formats, and many specialized scientific image formats. It has become popular in applications such as virtual microscopy and art imaging, and very popular as an image processing library for the web. This paper outlines the history of the library, explains how libvips achieves its good performance, presents benchmarks, and gives an overview of the implementation and of the wider libvips ecosystem.