The Cry It Out (CIO) Method is a sleep training method that requires you to let your baby cry and fuss for a set period of time before you take any action to intervene and soothe your little one. There are both proponents and critics of the CIO Method. It can certainly work for some babies but it may not be the best approach for others. When it comes to sleep training, it’s important to trust your parental instincts, try different methods, and find out what works best for you. Like so many things in parenting, there is no one right way to sleep train your little one.