The Gentle Leader Easy Walk Harness is designed to gently discourage your dog from pulling while walking on a leash. Unlike traditional collars, our harness never causes coughing, gagging, or choking because the chest strap rests low across the breastbone. Its unique front chest leash attachment stops pulling by steering your dog to the side and redirecting his attention towards you. And, its patent pending martingale loop provides extra leverage for easy, relaxed control and prevents harness twisting and gapping. Sizing: Petite ' for dogs with girth measurements of 12-16 inches Petite/Small ' for dogs with girth measurements of 14-18 inches Small ' for dogs with girth measurements of 15-20 inches Small/Medium ' for dogs with girth measurements of 19-25 inhces Medium ' for dogs with girth measurements of 20-28 inches Medium/Large ' for dogs with girth measurements of 25-35 inches Large ' for dogs with girth measurements of 26-36 inches Extra-large - for dogs with girth measurements of 34-46 inches.