Please measure your dog neck before ordering -Narrowest part of your dog's neck, which is behind the ears -The widest part of the head (circumference of the head) A martingale is a type of dog collar that provides more control over the animal without the choking effect of a slip collar. Martingale dog collars are also known as greyhound, whippet, saluki etc. The martingale dog collar was designed for sighthounds because their necks are larger than their heads and they can often slip out of buckle collars. These collars have gained popularity among owners of other breeds in the recent past with many trainers now recommending them instead of choke chains or buckle collars. A martingale collar is made with two loops. The larger loop is slipped onto the dog's neck and a lead is then clipped to the smaller loop. When the dog tries to pull, the tension on the lead pulls the small loop taut, which makes the large loop smaller and tighter on the neck, thus preventing escape. Properly fitted, the collar will be comfortably loose whenever the dog is not pulling against the leash.