The assessment of global pain in infants and children involves the analysis of subjective, behavioural and physiological components, beyond the psychological, familiar and environmental factors that influence and modulate the manifestation of painful symptom. Therefore, researchers and clinicians need valid and reliable instruments to obtain a correct measure of pain. Although subjective indices carry out a fundamental role in the assessment of pain (instruments adjusted to the age of the child), behavioural and physiological indices should be used when intelligence deficit or serious physical handicaps exclude such possibility. Behavioural aspects, associated and correlated to physiological changes, allow to obtain a reliable enough measure of pain. In this paper, the main instruments for measuring pain in infants and children will be described, and their advantages and disadvantages underlined.