Got 2 of these for our dog to wear after surgery - she had a large fatty tumor removed from her right chest wall. They worked out very well and the dog seemed to like them, too! She's about 40 lbs and is a mutt - possibly border collie and/or some type of spitz. I ordered larges and they worked out well. They seemed a little small around her chest at first, but it was mainly due to her fluffiness. We smushed that down and they fit fine. She normally doesn't wear clothes and doesn't even tolerate bows from the groomer for long, but I wanted to have something that would prevent her from licking at her incision.Initially, we let her rest upon returning home from the vet, and she was groggy and rather irritable with our cats, who she normally tolerates just fine. After she'd slept for a while, we started by laying one of these on top of her. She didn't love it but it didn't freak her out. One of the best things about these vests/coats is that you don't have to put them over the dog's head or put their arms through anything, so they're way less stressful to put on a dog that isn't used to clothes. The Velcro is strong and wide, plus the fabric is stretchy, so any given size should be able to fit a broad range of dog sizes. Also, having the Velcro at the chest and at the side allows the vest to accommodate different body ratios. Anyway, I worried that the pressure from the neoprene might be too much, but she actually perked up once this was put on. She was more willing to move around and her attitude toward the cats changed considerably. It seemed like it was because she knew the cats couldn't get to her incision anymore, so she relaxed with them.Overall I'm very pleased with my purchase and I don't know what we would've done without them. They've held up fantastically and still basically look new. I'm going to try to remember to put one on her the next time it looks like we'll get thunderstorms to see if it can act like a thundershirt. It had such a calming effect on her while she was so uncomfortable, I have high hopes.