The Ordonnance de Montpellier, signed on 28 December 1537 by Francis I of France, established the first legal deposit system.
In the Ordonnance, Francis decreed that no book be sold in France until a copy was deposited in his library. The decree was not widely followed and the legal deposit requirement abolished in the French Revolution.
References
Ordonnance de Montpellier Wikipedia(Text) CC BY-SA