<p>Everyone who endorses the categorial distinction between objects and events must confront a general question: how do these two types of entities relate to one another? Here we are especially interested in what is typically regarded as the basic relational tie between the two, namely, that objects may be said to participate or take part in events, whereas events befall or happen to their participants. The exact nature of this participation relation is philosophically contentious and may depend on how the two categories of objects and events are construed in the first place. Regardless of its metaphysical characterization, however, a number of questions arise concerning its formal features and the general laws that govern its behavior. In particular, since both objects and events can be mereologically structured, we are interested in the formal laws that govern the interaction between participation and parthood. If objects <i>are</i> events, as some perdurantists maintain, then participation just <i>is</i> parthood. But what if objects and events form genuinely distinct categories? What, then, is the relationship between being part of something and taking part in something?</p>