This article aims to examine the role of objects in the transformation of logics (Thornton & Ocasio, 2008) at the practice level. In particular, it explores how financial actors use, transform and are constrained by their ‘market devices’ – defined as a range of instruments, models and tools used by financial markets (Callon, Millo, & Muniesa, 2007) – when aiming to (re)design their logics and practices towards more sustainability. It develops a theoretical model based on ever expanding, institutional theory by combining it with practice theories. In particular, the article argues that actors transform their practices, logics and objects, by transforming an epistemic object through a collective inquiry. Empirical support is drawn from a three-year ethnography study of a French asset management company that attempted to (re)design its equity investment process, following new demands for Socially Responsible Investment (SRI). Research methods combine participative observation, semi-structured interviews and documentary evidence. Theoretical and methodological contributions are outlined for both institutional and practice theories.