SCION provides an implementation of the W3C SCXML draft specification in JavaScript. SCXML provides a declarative markup for Statecharts, a powerful modelling language for developing complex, timed, event-driven, state-based systems, and can offer elegant solutions to many problems faced in development of JavaScript-based applications across various domains. In the browser, SCION can be used to facilitate the development of rich, web-based user interfaces with complex behavioural requirements. On the server, SCION can be used to manage asynchronous control flow.