I wasn't sure what size to order and went with the s/m...i wear a size 10 shoe. Its a snug fit but works for me. The sock has some additional padding in the high wear zones like the toes and heel, and is thinner in other areas for breath-ability. There is also a high point at the back of the sock, kinda like a pull tab. That maybe be the intended purpose but i appreciate that it adds a layer of cushioning between the back of my ankle where i tend to get blisters when wearing low socks.I usually buy Under Armour or Bridgedale socks and i would say these are a fair priced compromise between the two: Under Armour is moisture wicking at a lower price while bridgedale does the thick/thin areas but at a higher price. I will purchase these again as an everyday sock as my UA's wear out, saving wear on my Bridgedale's for other adventures.