I initially purchased this vest in both a large and a medium and compared them (I'm a size 10).  The extra room in the large was primarily in the bust and armholes.  Not much extra room around the hips.  Since I intended to wear the vest at work, the larger armholes in the size large allowed the vest to ride up and poke me in the chin while sitting.  So I opted for the more form-fitting medium.  It took a little getting used to having such a snug fit, but the vest "gives" and the smooth fabric allows it to glide with the movement of my shirt.  It's contoured for a flattering fit, is cozy but not too warm indoors.  And I bought two more in size medium and have my eye on a fourth.  The Allegra navy and brown are very nice shades.