These tanks are my favorite.  I currently have a 38G bra size and the medium fits me well.  It provides good support without the need for an actual bra.  Don't expect it to hold you in place while running or bouncing but for layering it's perfect.  I am able to unclasp and clasp with one hand by pulling the shoulder strap down instead of pulling the tank part up.  I own this in 3 colors and will probably buy more!