Fredrik -> "With RIA Services you can't have entities cross domain services" That's because you must use an "all-in-one" solution.. and that's why I am going to build a multi domain service application. IMHO this could be the right way to build large application in an organized way. Fredrik -> "As more dependencies you have, as more you may need to change based on one single change." It is my point for multi domain service application. You have to admit that it is not an optimum solution. I thought it was my lack of experience but I find it is the way WCF RIA works. PS: Quoting here dosen't work the way I expected. I use Chrome on a Mac.