The regime perspective on long-term financial regulatory development suggests that regulations change as a pendulum between the theoretical poles of state and market. Periods of stability are punctuated by periods of instability when shifts between regimes occur. This thesis challenges that perspective by proposing that long-term regulatory development is better understood as a continuous process. Departing from institutional theory, the thesis argues that regulatory change is driven by changes in economic ideas as well as interest group influence. These two are interlinked, as interest groups continually work to promote ideas that benefit their interests. In three studies, the continuity and change of ideas and interest group influence of the Swedish Bank Act during the twentieth century are investigated. A fourth study looks at regulatory change during crises and external pressure by studying the Swedish capital controls from 1973 until their removal in 1989. Results show that the ideas underpinning the Swedish Bank Act shifted over time from conservative and moralistic to increasingly liberal, while its overall purpose remained stable. When the Bank Act was established, the Bank Inspection was the most influential institution. Over time, the Bankers’ Association could increase its influence over the Bank Act. In 1968, the banks succeeded in achieving large liberalizations of the Bank Act. The success of the banks in gaining increasing influence is explained by the ideas that were engrained in the Bank Act from its foundation. Even when regulations came under pressure and were adapted, the original ideas of the regulatory institution could not be abandoned. The results thus support that the long-term development of Swedish banking regulation is more a story of increasing interest group influence than that of a swinging pendulum.