A lot of companies are using or starting to use webservices and/or a Service Oriented Architecture. For each of these companies there comes a time to think about backwards compatibility and versioning. The solution is not always obvious. There are multiple options, we will discuss some of them and explain the concerns we have with them at our current projects. Our presentation deals mostly with a solution based on apache axis and the eclipse equinox implementation of the OSGi framework. The presentation uses a case of a congress registration system for demonstrating the problem of a plain webservice project. We will present our osgi based solution to the versioning problem. In a demo, we show that we can solve the versioning problem within one deployment with one ear/war file. Even better, we can do it at runtime, so no need to redeploy, no downtime. We can do an upgrade and roll it back without one second downtime. At the end of the presentation you will have basic understanding of osgi concepts. You will have the ambition to try it out yourself, that is when you take out your notes, go to our website and download all our material. This is when the real fun part starts.