This volume contains the proceedings of the 4th International Conference on Formal Modelling and Analysis of Timed Systems (FORMATS 2006), held in Paris (France) on September 25-27, 2006. FORMATS aims to be a major - nual event dedicated to the study of timed systems, uniting three independently started workshops: MTCS, RT-TOOLS, and TPTS. The ?rst three FORMATS conferences were held in Marseille (2003), Grenoble (2004), and Uppsala (2005). Timing aspects of systems have been treated independently in separate s- enti?c disciplines, and there is a growing awareness of the di?cult problems...