Abstract: We present a new data set on self-determination movements (SDM) with universal coverage for the period from 1945-2012. Our data set corrects the selection bias that characterizes previous efforts to code SDMs. We construct our measures of SD activity with other major data set s to illustrate advances in the conceptualization of SDMs as well as improvements in coverage. We add to the cross0country list of SDMs an events-data component that tracks a set of measures of SD activity, including governments’ policies towards SD movements. Our data allow us to study the escalation of SD conflicts over time and to reassess important theoretical arguments concerning separatist conflict that had been tested with incomplete or inferior data. We demonstrate the usefulness of our data set by revisiting Barbara Walter’s (2006a) influential argument that governments will not accommodate SD challengers if they face several potential challengers because they want to build reputation for strength. We find no support for Walter’s reputation theory of separatist conflict as there is no statistical relationship between the number of potential challengers and the level of government accommodation.