Many people don't fully understand the term "cosleeping," but they use the term nonetheless because most have a sense of what it is. Picture a mother lion and her cubs sleeping in a big heap, paws on top of backs, heads on bellies, body parts rising and falling with each rhythmic breath, the whole group intertwined in one peaceful lump of warmth and touching - that is cosleeping, or at least one version of it.

Of course, each species cosleeps uniquely in a manner reflecting the special biological needs and characteristics of its infants and mothers. For example, primates (including humans) typically give birth to one offspring at a time, providing each infant the opportunity to sleep alone with the mother or father. This way each infant can receive maximum attention during a very long and vulnerable infancy. Human infants are especially in need of a great deal of contact, emotional support, breastfeeding, and transportation.

Cosleeping refers to the many different ways babies sleep in close emotional and physical contact with their parents, usually within arms reach. Whether it is for protection, warmth, food, or comfort, humans and other mammals routinely sleep side by side, generation after generation. This book is about cosleeping, as practiced here in Western cultures and around the globe. In one way or another cosleeping remains universal for our species, predating history itself.

Cosleeping cannot necessarily be characterized the same way across all situations, but must be further broken down into safe and unsafe. And while each family's circumstances may vary, they can all be said to "cosleep" whenever they cuddle, snuggle and snooze together close enough to detect and respond to each other - whether on the same surface or not, and when at least one adult is committed to the infant's well being.

It is very important to acknowledge that cosleeping does not simply refer to bedsharing, for example, but it refers also to roomsharing, or any situation in which parents and infants are within arms' reach but not necessarily sleeping on the same surface. One of the difficult issues facing us is to reach agreement that while not all forms of cosleeping are safe, not all forms of cosleeping are dangerous, either. For example, some medical authorities mistakenly state that "cosleeping is dangerous," when they really mean to say that couch or sofa sleeping is dangerous (which is always true) or, that in their opinion, that bedsharing is dangerous (which may or may not be true, depending on how it is practiced). To speak about cosleeping without specifying what type of cosleeping one is referring to is to create more controversy and confusing than is necessary. While there may still be differences of opinion as to how to read the scientific findings on bedsharing (as I report below) there is generally much more agreement on some of these issues than it might appear.