content: I was on the fence about which size of sock to order, but I went with the SMALL rather than the medium and I think that was the right choice.My Vibrams are 40's and the small fit perfectly with my foot and the shoes.I've been using both steadily for about two weeks and have zero complaints.The socks are a must have to aid ease of use with the Vibrams, especially if you're the parent of a very young child who won't wait around while you figure out which toe goes where.