Hi! I had the same question this time last year. Service dogs are trained to perform tasks (IE: get your medicine, assist blind people with navigation, etc). Companion animals are primarily for comfort and support. Often times, dogs who aren't able to be service dogs will become companion animals. Because of the extensive training, there is usually a long wait and high price tag for service animals. You usually need a physician's prescription to get a service dog. That'll be important, if you're looking to have insurance cover the purchase. We got a companion dog. He's just what we needed. We're working on training him ourselves. So far, so good. I hope that helps. This place is pretty reasonable and has both (service and companion): http://www.pawsibilitiesunleashed.org/home