PHOEBE was conducted during the Berlin Ozone Experiment (BERLIOZ) between 5 July and 7 August 1998 near the city of Berlin. It aimed at a quantitative understanding of the fast radical chemistry in rural and suburban air by simultaneous measurements of the major free radicals (OH, HO2, RO2, and NO3) and the chemical compounds and physical parameters that control the radical concentrations. Interpretation of the measurements involved models of different complexity. The methods deployed and the results are discussed in the subsequent publications of this special section. This paper outlines the aims of PHOEBE, describes the observational site at Pabstthum, and briefly summarizes the different measurements and instrument comparisons as well as the main results of the accompanying publications.