This paper considers advantages and actual problems of web based simulation systems. Based on a review of environments and languages for web based simulation, some fundamental requirements for successful simulations are presented. The goal is to change the technology-driven approach in a more customer oriented philosophy. The common concept of "Application Service Providing (ASP)" should be understood as a future technology for web based simulation environments. The paper presents a real Simulation ASP. The system is based on a database for all model and simulation data. Different simulation tools are permanently linked to the ASP control system and provide the end-user with a highly interactive work. Three different levels of modeling (source code, fixed models and universal simulation components) lead to high flexibility for all areas of simulation.