I wear an 11 but ordered one-half size bigger because I thought they would be easier to slip into. Wrong! So I exchanged them for 11's and they fit just right. The larger boots slid up on my heel with each step and the only way to cure that annoyance was to wear very thick socks which I don't like to do. The 11's fit just right with thin socks. I just went on a 5 mile walk with my dog, through the snowy woods here in the Philadelphia area, with the temperatures in the low 20's and I didn't feel any cold or moisture. I even forgot I was wearing them which I guess is the goal. I have a pair of lace-up 34 year-old Sorels and they still work great but these slide on and off so much easier and give the same great performance. I suppose these will literally last me into my mid 80's!