Heart rate variability (HRV) has become the focus of interest of a multitude of investigations being a parameter that can easily be recorded. Accepted clinical indications in adults include evaluation of diabetic neuropathy and prediction of prognosis after myocardial infarction in adults. In children, HRV is regularly being registered in the pediatric sleep laboratory in sleep related breathing disorders, after apparent life threatening events, or in infants with assumed increased risk for sudden infant death syndrome. However, uniform interpretation criteria have not been established in these situations, at least partially due to insufficient understanding of physiology and pathophysiology of HRV in this age group. In this overview, current knowledge on HRV in infants and children is summarized and its clinical relevance discussed. In addition, technical requirements and methods of analysis which have a major impact on calculated parameters are being presented.