A comprehensive review of the evidence documenting preterm infant physiologic responses to Kangaroo Care (KC – intermittent skin-to-skin contact) and Kangaroo Mother Care (KMC – 24/7 skin-to-skin contact) has been conducted. Kangaroo Care's effects on preterm infant heart rate, bradycardia, respiratory rate, apnea, oxygen saturation, cerebral oxygenation, supplemental oxygen needs, oxygen consumption, desaturation episodes, temperature, rewarming, blood glucose, serum bilirubin, cholecystokinin, gastrin, somatostatin, weight gain or change, sleep and crying, brain maturation and complexity, infection, stress, and pain are reviewed, as are KC's effects with congenital heart defect infants. Documented effects of KC on prevention and amelioration of maternal depression, swifter delivery of the placenta and involution, and decreased likelihood of postpartal anemia are presented. Guidelines based on dosage (duration and frequency) of KC are provided, as is a summary of actual and potential benefits of KC, including use at end-of-life. Kangaroo Care's role in moving to the new paradigms of non-separation of the infant and mother during hospitalization and parents as primary providers of neonatal care concludes the manuscript.