Article dans une revue: Contrary to what law and finance theory would predict, the Paris Bourse was highly liquid at the turn of the twentieth century: the traded volumes amounted to four times the French GDP. This magnitude was mainly due to forward trading. The Bourse had developed as a forward market, despite a ban on forward transactions. The guild-like body running the Bourse played a key role in legitimizing and legalizing these operations, previously equated with gambling. The 1885 legalizing act initiated a new field of law (‘securities law’) and paved the way for the heyday of the Paris Bourse.