While the need to version a service is still to be debated, one aspect which we all need to accept is that services need to be maintained in multiple variants to satisfy multiple classes of consumers. Service request can be enhanced to include additional information which will help providers to apply rules to route requests to the appropriate class or variant of the service. While it is tricky to handle this kind of routing using a trivial handler or interceptor-level, an ESB provides you all the required design patterns and hooks to enforce content-based routing. Then neither the service provider nor the service consumer needs to be aware of these complexities. These design patterns and hooks are grouped under the broader heading of EIP and the next chapter is going to look at them in greater depth, again with working code samples.