A great number of daylighting research activities including investigations of innovative daylighting systems, lighting controls, and development of daylighting design tools are being conducted in Australia, North America, and Europe. There is a strong need for coordination and sharing of the experience from these activities, and for transformation of the achievements into practical building design guidance. International collaboration is necessary for the establishment of procedures for the characterization and evaluation of daylighting and lighting control system performance under the very diverse nature of sky conditions throughout the world, and it was on this basis that IEA Task 21 started in 1995. Task 21 is a comprehensive collaborative research effort, involving more than 40 institutions from 16 IEA countries, under the Solar Heating & Cooling Programme of the International Energy Agency. The paper reports on the work of this huge international daylighting Task, with only 12 months to go of irs four-year duration, describing how the work hopefully will influence on future building design.