This article presents an empirical analysis of a unique dataset of 1240 former members of the Provisional Irish Republican Army (PIRA). We highlight the shifting sociological and operational profile of PIRA's cadre, and highlight these dynamics in conjunction with primary PIRA documents and secondary interview sources. The effect of these changes in terms of the scale and intensity of PIRA violence is also considered. Although this is primarily a study of a disbanded violent organization, it contains broad policy implications beyond the contemporary violence of dissident movements in both Northern Ireland and the Republic of Ireland. We conclude with a consideration of how a shifting sociological profile impacts upon group effectiveness, resilience, homogeneity, and the turn toward peaceful means of contention.