THIS NIGHT has 3 sizes: S/M, M/L, and XL
S/M socks (on the right foot below) fit women's shoe sizes 4 to 10½ and men's shoe sizes 5 to 9. They really do fit both ends of the spectrum, so don't worry if you have small feet (the heel won't go up!) or larger feet (my mom is a 10½, and she can wear the S/M comfortably!).
M/L socks (on the left foot below) fit men's shoe sizes 7 to 13 (except for the KYOTO style, which fits up to an 11) and women's shoe sizes 8½ to 14. The foot part is a little bigger, the band is slightly wider, and the socks are about 2½ inches higher than the S/M. You can see from the photo below that both sizes give plenty of leg coverage.
If you like short socks, please take a look at the Ankle Sock offerings (available in both S/M and M/L). These are cuffless and have enough sock so that they show and won't slip down into your shoe but are a nice option for hot weather or if you have sensitive ankles.
If you'd like taller socks, THIS NIGHT makes those, too: S/M Knee/Boot Socks (a true knee sock –– this will go right under your knee) and M/L Knee/Over-the-Calf (as they are called in the world of hosiery) Socks.
And finally, if you wear a men's 14 to 18 shoe size, by popular demand, THIS NIGHT now makes XL socks, too. (Right now, in STRIPE and SUBWAY.) The height is the same as the M/L, but the foot part is bigger.
Please email me if you have any questions!