I wasn't sure about the sizing, as I have athletic thighs and glutes (hence wanting these to wear with my workout clothes), so got the medium, even though I think a small would have worked.  (I'm usually a size 2 to 4, depending on how stretchy things are, but my waist is about 27 inches, so not that small).  They are very comfortable and the legs stay in place pretty well.  I like boy legs to wear under leggings as they don't leave panty lines.  They wick sweat well and felt good to wear around the house before my workout.