This paper explores the organizational dynamics of Enterprise Risk Management (ERM). ERM is the main form taken by firms' increasing efforts to organize uncertainty, which 'exploded' in the 1990s. The ERM approach seeks to link risk management with business strategy and objective-setting, entering the domains of control, accountability and decision making. In this work, the organizational variations of ERM are investigated through a longitudinal multiple case study, using data from three companies collected over a 7-year period (from 2002 to 2008). The findings contribute to our understanding of ERM as a practice, revealing its trajectory within the organizations as it encounters pre-existing logics, and as both are shaped by risk rationalities, experts and technologies.