With Web Services, companies have now access to a simple, free and stan- dardized technology that allow them to open cost effectively their information systems. We are trying to design solutions in order to let them expose sensitive data and processes to distant business partners via the Internet. Therefore, with a special interest for security and reliability issues, we have focused our work on two main questions: how to safely expose web services over a public network? How to control the ever-growing number of invocations for these ser- vices while providing a constant level of service? Indeed, the more WS will be used (especially thanks to new consumption models), the more actors will ask for transparency at runtime highlighting a strong need for built-in quality of service (QoS) features. The first part of our work was to design a secured architecture for exposing business web services over the Internet. Then, we have proposed several inter- action modes between composite web applications and enterprise services based on state-of-art web technologies (asynchronous communication between client and server, usage of emerging formats like RSS). Finally, we have implemented a system that evaluates QoS metrics from different ”points of view” in a Service Oriented environment.