This study considers the genesis and development of two stock markets established in London in 1995. It draws on elite interviews and documentary sources to explore how the founders of these markets sought to legitimize them as stable, durable venues for security trade. The study uses insights from the STS-inflected study of markets to present an account of legitimacy as embedded in taken-for-granted socio-material structures. We term this phenomenon 'silent legitimacy'. Contributing to a nascent 'material turn' in institutional theory, we argue that the markets-as-institutions literature can be strengthened through attention to the mundane material dimensions of institutional fields.