According to a traditional view about the ontology of biological taxa, taxa are natural kinds with kind-specific essences. This view has been challenged by different types of arguments by both biologists and philosophers. However, in opposition to these arguments, philosophers have recently argued that biological taxa do contain essences if we further refine the traditional notion of biological essence. These new versions of essentialism are distinguished by how this refinement is carried out. According to Okasha’s (2002) essentialism, essences are relational rather than intrinsic properties. For LaPorte (2004) and Griffiths (1999), essences are certain ancestor-descendant relationships. Sober (1980) suggests that Kripke’s argument for origin essentialism might be extended to biological species. Devitt (2008) and Boyd (1999a,b) allow essences to be clusters of properties—rather than single properties. The arguments for these new forms of essentialism are based on assumptions informed by current biological systematics. For instance, whereas Okasha’s argument is based on species concepts, LaPorte’s and Griffiths’ essentialisms rely on cladistics. The goal of my dissertation is to identify these assumptions and examine whether they can be used to substantiate biological essentialism. I argue that they cannot: theories in biological systematics do not support the view that biological taxa contain essences. However, by simply rejecting essentialism we are left with unanswered questions that essentialism was designed to solve, such as explaining the presence of a certain trait among conspecific organisms. For this reason, in the final chapter, I consider some possible directions as to how we can address the problems essentialist theories were designed to solve without assuming that biological taxa contain essential features. Moreover, since arguments for biological essentialism are typically inferences to the best explanation, in considering non-essentialist alternatives I cast doubt on whether essentialism provides the best answers to some questions about biological taxa.