 There are many senses in which a thing may be said to be fundamental—some technical, some relatively intuitive. A very common way to think about fundamentality is in terms of independence, whereby for any notion of dependence D, an entity is D-fundamental if and only if it does not dependD on anything else (or on anything else that does not depend on it). This independence-based characterization of fundamentality will be discussed in sections  1.1  and  1.2.  There are also other ways to understand fundamentality; these include fundamentality as a complete description of reality  (section 1.3)  and as primitive  (section 1.4).  So, there are many ways to understand fundamentality and whether there is any single idea of fundamentality that these different ways are trying to capture is a substantial issue. But even if there is no unified sense of fundamentality, one interesting question is whether there are any fundamental entities, where “fundamental” is understood in one of the different ways that will be specified below. We might also ask whether we need such entities, whether given theories are committed to their existence, and what the role of fundamentalia is in explanation. Before we get started, a few preliminary issues need to be mentioned.