I just got these today and have been wearing them. I bought both a Medium and a large. My past experience with Thorlo socks are that they are very comfortable and well made, but they seem to run on the small side. I wear a Women's size 10 in shoes. This Medium sock is supposed to fit women from size 9.5 to 11.5, but for me they are too short and put too much pressure on my toes if they are fit properly in the heel area. For me the large is feeling much better. Other that figuring out the sizing, these appear very well made and are very comfortable socks. And the color is pleasant too, very nice for spring!