Amongst the world population, there are people who suffer from certain phobias. Those can be of different levels and sometimes be so severe that they can lead to mental disorders. A person suffering from phobia can treat its disorder effectively by using short term exposure therapies. Those consist of confronting the feared object or situation, directly. The therapies increase in intensity over time until the patient habituates. An example would be, confronting an arachnophobic person with a small spider on the first sessions before enlarging it and making the patient approach it on the following ones. The issue with giving such a treatment in vivo can be tricky in two ways: it is sometimes unpractical for psychotherapists to make the feared situation available to their patients and, furthermore, patients are often so scared of their phobia source that they are not willing to participate in an in vivo exposure therapy. This is where virtual reality comes as a solution. Indeed, during this project, literary researches have been made in order to get knowledge in this domain. It has been learnt that virtual reality exposure therapies are indeed an alternative to classical exposure therapies and that patients can benefit from them. The advantage of virtual reality therapies is that they solve the problems related to conventional therapies. The goal of this Master Thesis was then to develop a virtual reality application that could be used in order to treat acrophobia and arachnophobia. The app has thus been designed and developed carefully to maximize its user friendliness but also to allow therapists to control the therapies. The app is therefore “played” in an asymmetrical way, where the patient puts the VR headset and undergo the therapy while the therapist controls the virtual world (e.g. the size of the spider or the height of the elevator) in real time.