I went with a large because I wasn't sure if a medium would be too tight. While I quite like the fit of the large, I might go ahead and try medium next time. If you're between sizes bust-wise, you *might* be okay sizing down, depending on the look you're going for. I bought both this green and blue and I can see these tees becoming favorite go-to wardrobe staples. Very soft, very comfortable, and will go with all the things!