When do babies sleep all night? When will my baby sleep through the night? When will my baby sleep longer at night? These are all popular questions that bring many of you to The Baby Sleep Site®, looking for answers. And they are questions that we'll be tackling in today's blog post! What Is Sleeping All Night Exactly? As always, we have to get our terms straight when we are discussing sleeping through the night. Remember, the medical definition of 'sleeping all night' is just 5