very cute little harness and a great design. i got this for my bichon puppy when she was 3 months old, 6 pounds. The XXS fits my pup on the smallest adjustments setting. The harness has a fabric portion that is kind of like a sleeveless shirt. it is attached to nylon straps at the "arm holes" and "waist area" that adjust to give a fairly custom fit that will hug your dog. My pup is still using the harness now at 5 months and 7.5 pounds and I haven't had to readjust the settings yet, to give you an idea of its range. The harness straps are adjustable to a pretty large range, so I think I might be able to use this harness for my pup to full maturity. The best part is the convenient and easy on and off. From the front, you just slip the front paws in and snap the buckle on the back-- to take off, just open the buckle on the back and the harness falls off. I feel like this harness is sturdy and the design is secure. My pup has not shown signs of being able to slip out of it, like she has with another harness I tried. The fabric was a little stiff at first, but I put it in the wash and it softened up a bit to be more comfy.one caveat is that the nylon adjustable strap part which also holds the buckle on the back of the harness is 3/8" thick, which feels a little thin. i feel like it might dig into the dog's skin when they tug. but so far, my dog seems fine wearing it though.UPDATE: my pup is now full-grown at 9.5 pounds and can still use this harness on its largest setting. i might order the XS though since the nylon back straps are 5/8" thick on that, which i think might feel more comfy!