This thesis presents the development and evaluation of a prototype serious computer game to provide social skill training for young adults and adults with High-Functioning Autism. Autism is a neurodevelopmental condition changing the way people see the world and interact with others. It occurs on a spectrum of severity, with individuals at the less severe end classified as having High-Functioning Autism (HFA). Individuals with HFA present above average intelligence but socio-communicative deficits in non-verbal and verbal behaviour. As individuals with HFA transition into adolescence and adulthood, they struggle to sustain education, employment, and social relationships. Socio-communicative deficits can be positively addressed through social skills training interventions, designed and delivered by behaviour therapists. However, these therapies are not readily available to most individuals due to the intervention costs and shortage of specialized therapists. Computer interventions designed to address socio-communicative deficits among children, adolescents and adults with HFA show promising results. One style of intervention is the serious game format. Serious games are designed to deliver learning outcomes, but present as games, and so typically have greater appeal than overtly pedagogical software. A game was created in Unity 3D as a first-person view of a restaurant environment and experience. In the game, the participant walks into a restaurant, interacts with a greeter, is led to a table and seated, and is joined for dinner by a friend. The game integrates features from social skill training interventions with the interactive experience, addressing multiple social skills. Evaluation of the game for its effectiveness and usefulness for social skills training showed that it provided a plausible learning environment, in that it raised awareness of skills and neurotypical behaviour, and it reduced anticipated anxiety for most trial participants towards future situations in which the social skills might be needed. The level of realism achieved was not demonstrated to be sufficient to provide a fully immersive experience particularly with respect to the skill of making and maintaining eye contact. Further work is required to make the serious game sufficiently realistic to provide a complete training experience, and to find out if the training it offers can be transferred into real world interactions.