Despite its importance as a financial centre, the historical literature dedicated to the Swiss financial industry remains scarce. Analyses focusing on cantons and cities of the country are even more limited in number. This is unfortunate and is, in all likelihood, linked to the reluctance of financial institutions to share information in a country where banking secrecy has been at the core of the past success of these institutions. Despite this willingness to share as little as possible, some archival funds have gradually become available, most notably after businesses went bankrupt, changed hands, or simply disappeared. The present article relies on these sources to analyse the evolution of the Geneva stock exchange during the interwar period, which saw a gradual decline of its activity. Independent brokers strived to keep their oligopoly over banks. At the same time, Swiss German banks tried to penetrate the canton-controlled marketplace by using their federal rights and strength to become unavoidable actors. They could ultimately help local bankers gain direct access to the Geneva stock exchange, obliterating the power of brokers who were left with no other choice than to appeal to the Canton of Geneva to defend their position.