Scwm is the Scheme Constraints Window Manager, a highly dynamic and extensible window manager for the X Window System. Scwm embeds Guile Scheme as the configuration and extension language, and includes a sophisticated constraint solver for permitting the user to interactively specify constraints among top-level window sizes and positions. Nearly all decorations can be changed at runtime on a per-window basis. Dynamic loading of C modules is supported. Scwm is self-documenting and provides a powerful protocol for interacting with the window manager from other processes.