A multi-functional adjustable tray that mounts on the arm of a chair to provide a comfortably accessible work surface to support a computer mouse and other IO devices. The adjustable tray may be easily mounted to an arm of a chair and provides width, length, rotation, and storage adjustments. The adjustable tray includes a platform that is pivotally connected to an armchair stop. The armchair stop may be supported by adjustable guides that may be secured to the chair arm by a compression element. The tray may include one or more rotatable joints to allow the platform or IO devices to be tilted to a comfortable working angle.