If my dog understood performance outerwear, he would love this jacket.It's a slim fit, so he walks funny for a bit when it first goes on, but once we are outside, he forgets it's on. He likes to run through the woods, chasing scents & small critters, and this jacket has never snagged on a branch, and doesn't show any signs of wear at all! Also, in deep snow, it prevents "snowballs" from forming on his belly & upper leg fur. It keeps him really warm as well! It's really well made, with a soft fleece lining, a stretchy under panel, and a weather resistant top panel.I've read reviews of this jacket in which people complain about the zipper coming undone. The key is to flip back the zipper once its all the way zipped, as it has an auto locking mechanism built in.As far as sizing, my dog is skinny but long (60-lb lab/hound), so he fit in to a medium for the chest measurement but a large for length. I went for the medium, and it has worked out well (see picture).I've tried a few jackets on my dog, and this is my favorite. It doesn't restrict his movement, and it hold up well to (dog) abuse! I recommend it!