The CoyoteVest is compatible with most simple step-through harnesses. It's just a matter of putting the harness on after the vest. You must still use a collar with the vest in order to secure it around your dogs neck, but if you prefer a harness can be used for the leash attachment. If your looking for a new harness that is proven to work well with the CoyoteVest, these will do the trick. These are designed for small dogs and are very dainty and lightweight. We have a larger harness available here. These harnesses are made in bright day-glow colors that match the CoyoteWhiskers. You can mix-and-match our bright colors any way you like! We also added a reflective safety strip so your dog will be more visible at night. *There may be a variance in the reflective tape. And to make our harness even nicer we include a matching leash. Sizing Chart Harness Size Chest Size Webbing Small 12" - 18" 3/8" Medium 16" - 24" 5/8" Measure dog without vest on to get accurate measurements. Measure the circumference of your dog’s body behind the front legs and around.