In almost all armed conflicts, mass population displacements, natural disasters and other crises, a number of children become separated from their families or from other adults responsible for them. These children form one of the most vulnerable groups in these situations, often deprived of care and protection. Most can be reunited with parents, siblings, members of the extended family or other adults whom they know and who are willing to provide for their care. Action on behalf of unaccompanied and separated children should be guided by principles enshrined in international standards. The validity of these principles has been confirmed by experience and lessons learnt from conflicts and natural disasters in recent years. This publication outlines the guiding principles which form the basis for action in this regard: a comprehensive approach; preserving family unit; tracing and family reunification; care arrangements; durable arrangements; special issues related to refugee children; and promoting children’s rights.