The question ‘What is Consent?’ is commonly understood as a question of what the concept of consent refers to. Two main positions can be distinguished. Whereas the Mental View takes ‘consent’ to refer to a mental state of the consenting agent, the Performative View holds that it refers to a public action. As the proponents of the latter view normally emphasize that ‘consent’ understood as a public action must be given with an adequate, ‘consenting’ mental state, the so-called debate on the ontology of consent is best understood as a debate on whether having a consenting mental state alone is constitutive of consent or whether the communication of consent forms a constitutive part of consent as well. The chapter introduces and discusses the Mental View and the Performative View and the main arguments put forward for them, respectively. It also considers the possibility of distinguishing between three main views instead. The third option, the so-called Hybrid View, combines the core elements of the Mental View and the Performative View. Furthermore, the chapter explores what may turn out to be hard cases for each of the two main views.