I have a WCF service that supports about 10 contracts, we have been supporting a client with all the business rules specific to this client now we have another client who will be using the exact same contracts (so we cannot change that) they will be calling the service exactly the same way the previous client called now the only way we can differentiate between the two clients is by one of the input parameters. Based on this input parameter we have to use a slightly different business logic – the logic for both the Client will be same 50% of the time the remainder will have different logic (across Business / DAL layers) . I don’t want to use if else statement in each of contract implementation to differentiate and reroute the logic also what if another client comes in. Is there a clean way of handling a situation like this. I am using framework 3.5. Like I said I cannot change any of the contracts (service / data contract ) or the current service calling infrastructure for the new client. Thanks