They have a built in underwire bra, see:
You order them by your bra size. I love them so much! I wear them with cardigans and a scarf to the office. I wear them by themselves on the weekends. I only have the two right now, but am waiting on four more to arrive anyday now. Here is where you can buy them: Solutions.com. I bought the ones that are half off, the neckline is a bit higher than I would prefer, but the price is right. If you do an online search you can find coupon codes for free shipping. These are going to be the basis for my new wardrobe. Oh ,by the way, do not put them in the dryer.