The article is devoted to some historical and legal aspects of customary law of the ancient Celts. It has been proved, that legal customs were one of the factors consolidating disparate Celtic tribes — the Gauls, Galatians, Helvetians, Britons, Belgs and others. The annual election procedure of Celtic tribes of their political leader (verhobret) has been researched. The legal nature and peculiarities of the judicial powers of the Druids have been founded. Conditions of fights and robberies, which were allowed by Ancient Celts customary law, have been analyzed. Procedure and legal implications of Celtic clientele have been reviewed. The specific features of posthumous loan`s agreement have been highlighted.