What is the effect of protest mobilization on democratic transition and durability? This dissertation argues that protest mobilization increases the odds for a democratic transition, but it is the length of the mobilization that matters for the durability of new democratic regimes. In particular, sustained unarmed uprisings have generated the longest-lasting new democracies – largely because they are forced to develop an organizational structure that provides a leadership cadre for the new regime, forges links between the government and society, and strengthens checks on the power of the post-transition government. I use quantitative methods, comparative case studies, and a detailed case study of Egypt to demonstrate this argument.