Update: I ordered a medium, because the large was a little big, but after getting it, it was way to small. So returned it. Customer service was great and was refunded the day I post marked it. No hassle at all. Have had one for three months now and the dog caught it on a wire and tore it up, but I have ordered two more. Wife absolutely loves these and will not consider any thing else. I had to update to 5 stars, just because of customer service. A little alteration may be needed to fit the neck of different dogs, and it will slip if the dog pulls backwards on it, but it holds well as long as they pull forward. Wouldn't suggest for a dog that fights the harness, but its great for a half way disciplined dog.I ordered a large for miniature schnauzer with a 21 inch chest (measured). Dog has worn it about a week and it keeps sliding over her head and will go no tighter, whether its stretched or just to large I'm not sure, but we ironed patches onto it which makes it non returnable. Wife loves it except too big, we're biting the bullet on this one and have ordered a medium, but according the the size chart on the website it may be too small. Don't think whoever sews these things care about accuracy.