Lukas Jenni was born in Basel, Switzerland, in 1955 and became interested in birds as a boy. While studying zoology, botany, geology and chemistry at Basel University, he became a volunteer at the Swiss Ornithological Institute and a ringer at Col de Bretolet, where his interest in moult and ageing arose while working with Raffael Winkler. He graduated with a study on the morphology and ecology of Great and Middle Spotted Woodpeckers. In 1979, he became head of the Swiss ringing scheme at the Swiss Ornithological Institute and gained his PhD in zoology with a study on the mass concentrations of Bramblings in winder in 1984. His main research interests are in ecology and the physiology of bird migration, as well as in moult biology. Raffael Winkler was born in 1949 in Basel, Switzerland. Interested in birds since his early childhood, a stay at the Station Biolgique de la Tour du Valat in the Camargue convinced him to study zoology. At the University of Basel he attended lectures in zoology, botany, paleontoloy and psychology and graduated with a Ph.D. thesis on the pneumatization of the skull roof in birds. The data for this study were collected at the ringing station at Col de Bretolet in the Swiss Alps, where he also began a close co-operation with Lukas Jenni in the fields of passerine moult, aging and bird migration. From 1975 to 1980 Raffael was employed at the Swiss Ornithological Institute, managing the avifaunal information centre and cultivating contacts with amateur birdwatchers. During this time he was secretary of the Swiss Rarities Committee and worked on the Atlas of Breeding Birds in Switzerland. In 1980 he was elected curator of the bird collection at the Natural History Museum, Basel. Since then, he has edited the Avifauna of Switzerland and carried on the Museum's own tradition in moult research.