ABSTRACT Building on the author’s book Nationality of Foundlings (Springer 2021), this article examines the definition of the term ‘foundling’ under Article 2 of the 1961 Convention on the Reduction of Statelessness, with particular focus on the most commonly debated issue: The maximum age of the child when found in the territory to qualify as a foundling. It first asserts that the grant of nationality to foundlings is a customary international law norm. The article then advances an evolutionary and teleological approach to interpreting the 1961 Convention in light of its objective of reducing statelessness, considering the development of human rights law and best state practices. The analysis of the travaux and the comparison of the nationality laws of 193 UN member states (of which 142 states have foundling provisions) first clarify that the term ‘foundling’ means ‘a child of unknown parents. Further, it reveals that foundling provisions of 10 states (7% of 142 states) explicitly cover all minors of unknown parents, and that the provisions of at least 16 states (11%) encompass all minors according to available legal interpretations. This is exemplified by legal precedents in which Spain and Italy, respectively, recognised minors who were around 11 and 12 years old when found in their territories as their nationals under their foundling provisions. In light of Article 7 of the Convention on the Rights of the Child and the best interests of the child, this article concludes that the term ‘foundling’ is not restricted to a ‘newborn child’ or a ‘young child’ but covers all minors of unknown parents. KEYWORDS Statelessness, Foundlings Definition, Child of Unknown Parents, Abandoned or Orphaned Children, Unaccompanied or Separated Children