Bought a harness for my 14 week old Red Fox Labrador. Had to speak to customer services before ordering as fitting dogs under one year can be problematic. The harness comes in 3 pieces . Front, girth and top. Had to change girth for larger size so puppy now has: front - XS, girth - medium and top - small. I would never have managed to get a good fit from any other harness as they sell all pieces the same size. Apart from a well fitted harness I can order additional pieces so as my puppy grows I only need to replace the relevant piece rather than the whole harness.