Ventilation is pivotal both in terms of indoor air quality and environmental issues such as greenhouse gas emissions. It also has a major impact on energy use in buildings. It is important, therefore that the role md impact of ventilation is filly understood. The purpose of this paper is to review these aspects with particular reference to recent research and developments. Key aspects are concerned with the role of ventilation in maintaining good indoor air quality, ensuring the quality of the outdoor air and incorporating strategies to ensure good ventilation performance. References are particularly made to the development of standards and to examples of good case study buildings. Although good progress is being made, areas that still need to be addressed include maintaining good outdoor air quality and preventing contaminated outdoor air fi-om entering buildings.