This is the perfect car booster seat! I purchased the small medium size for my 20lb Pug and he fits perfectly in it as it’s big and spacious. The car seat belt securely loops through the backside and keeps the booster in place and a small leash on the inside clips to his harness to keep him safe. The booster itself has high walls which my Pug likes to rest his head on and a tiny pillow on the inside keeps him comfortable. I recommend to make sure you push your car seat back as far as it goes in the event that the cars airbag ever deploys.