In this chapter I look in detail at essences and essentialism in biology, with a focus on species essences. These are among the implicit entities of science belief in which requires at least the MoS stance. I outline and defend a particular account of what essences are: sets of properties that are, and must be, possessed by all and only members of the kind they define (or all and only parts of an individual they compose). I then use this account to classify several prominent views on the metaphysics of species as essentialist or non-essentialist, in a way that runs counter to the way some of these views tend to be construed. For instance, on this account the species-as-individuals view turns out to be an essentialist view, and the homeostatic property cluster account turns out to be a non-essentialist view. This will, in turn, enable us to identify the underlying epistemic stances that are required for different views on species, metaphysics, and essentialism.