 When it comes to the metaphysical underpinnings of scientific theories, properties play a prominent role: it appears that science can hardly be done without appealing to them. This adds up to the case for realism about properties and to our understanding of them. We shall illustrate this here first by dwelling on some miscellaneous topics and then by focusing on a debate regarding the very nature of the properties invoked in science, namely whether or not they are essentially dispositional. Roughly, an object exemplifies a dispositional property, such as soluble or fragile, by having a power or disposition to act or being acted upon in a certain way in certain conditions. For example, a glass’ disposition of being fragile consists in its possibly shattering in certain conditions (e.g., if struck with a certain force). In contrast, something exemplifies a categorical property, e.g., made of salt or spherical, by merely being in a certain way (see entry on  dispositions).