Pain is a phenomenon so common that almost all individuals become familiar with this sensation at some point in life. Some consider it as unavoidable and others as a challenge that has to be defeated. During the second part of the last century researchers became interested in the neurobiological source and regulation of pain, the use of assessment instruments to “objectify” pain, and treatment options for distinct patient groups and types of pain. Meanwhile we have become aware of the negative impact of pain on quality of life, recovery from surgery and survival, as well as the risk of acute pain turning into chronic pain. Babies and intellectually disabled individuals of all ages have often been excluded from pain studies; for long it was believed that they were unable to experience pain. For infants and young children this belief was not specifically based on a scientific rationale but more on a lack of knowledge about the status of the myelinisation process of the nerves in neonates, the individual variability in drug disposition and fear of harmful side effects of analgesics and narcotics. Intellectually disabled individuals have always been considered to be unable to experience or suffer from pain. This misconception was partly based on absence of visible emotion during potentially painful situations, like continuing to walk with a broken hip or leg. Such observations seemed more important than the knowledge that a condition is known to be (extremely) painful in individuals that are not intellectually disabled. Fortunately enough we have done away with these misconceptions. A landmark publication of Anand and Hickey in 1987 reported huge circulatory and metabolic complications in (prematurely born) neonates after ligation of a patent ductus arteriosus without fentanyl compared to children that received fentanyl. Since then it was acknowledged that babies are capable to feel pain and require treatment just like in older patients.