The risk of Sudden Infant Death Syndrome (SIDS) has fallen dramatically in the "Back to Sleep" era; however, half the cases now occur when the infant has been sleeping in bed with another person. Despite the association of SIDS with co-sleeping, parents are receiving mixed messages. It is often presumed that co-sleeping deaths are due to 'overlaying', when the adult rolls on top of the baby, stopping baby from breathing. We examine research that shows that it is not necessary to cover the face, or squash the body of a baby to restrict or prevent breathing and cause oxygen deprivation. At birth, the temporo-mandibular joint is not yet fully formed, and thus the jaw can be easily displaced upwards and backwards pushing the tongue into the upper airway to form a partial or complete block of the airway. Indeed, this can happen with firm flexion of the infant's head so that the chin pushes against its own chest. Further research is needed, but on present evidence, all parents should be advised to sleep their baby in a cot or similar next to their parent's bed, until baby is at least 6 months of age.