The previous chapters on interaction dynamics, the central aspect of the second part of this volume, have investigated the determinants of various action forms of the contending parties as a function of preceding action types or contextual features of the episodes. One particular feature of these dynamics, however, has remained unexplored. The flow of interaction between the contending parties does not proceed in a smooth, linear fashion – with one action triggering a reaction that in turn triggers a counter-reaction – as a stylized understanding of contentious politics might suggest. As we have shown earlier in Chapter 6 on the construction of action sequences, the empirical reality paints a more complex picture. While some actions indeed trigger one and only one further action and move the episode forward in that stylized fashion, others trigger two or more reactions, while still others put an end to a sequence and trigger no further actions at all. In other words, some actions have turned out to be considerably more consequential for the remaining part of the episode than others. Our first aim in this chapter is to highlight one type of such actions, in particular those with a heightened capacity to trigger an outstanding number of reactions, and seek to understand the regularities that characterize these actions. We shall refer to these actions as points of opening, inspired by the intuition that they open up contentious episodes to different threads of contention.