The Basel UrBan Boundary Layer Experiment (BUBBLE) was a year-long experimental effort to investigate in detail the boundary layer structure in the City of Basel, Switzerland. At several sites over different surface types (urban, sub-urban and rural reference) towers up to at least twice the main obstacle height provided turbulence observations at many levels. In addition, a Wind Profiler and a Lidar near the city center were profiling the entire lower troposphere. During an intensive observation period (IOP) of one month duration, several sub-studies on street canyon energetics and satellite ground truth, as well as on urban turbulence and profiling (sodar, RASS, tethered balloon) were performed. Also tracer experiments with near-roof-level release and sampling were performed. In parallel to the experimental activities within BUBBLE, a meso-scale numerical atmospheric model, which contains a surface exchange parameterization, especially designed for urban areas was evaluated and further developed. Finally, the area of the full-scale tracer experiment which also contains several sites of other special projects during the IOP (street canyon energetics, satellite ground truth) is modeled using a very detailed physical scale-model in a wind tunnel. In the present paper details of all these activities are presented together with first results. The Basel UrBan Boundary Layer Experiment (BUBBLE)was a year-long experimental effort to investigate indetail the boundary layer structure in the City of Basel,Switzerland. At several sites over different surface types(urban, sub-urban and rural reference) towers up to at leasttwice the main obstacle height provided turbulenceobservations at many levels. In addition, a Wind Profilerand a Lidar near the city center were profiling the entirelower troposphere. During an intensive observation period(IOP) of one month duration, several sub-studies on streetcanyon energetics and satellite ground truth, as well as onurban turbulen and profiling (sodar, RASS, tetheredballoon) were performed. Also tracer experiments withnear-roof-level release and sampling were performed. Inparallel to the experimental activities within BUBBLE, ameso-scale numerical atmospheric model, which contains asurface exchange parameterization, especially designed forurban areas was evaluated and further developed. Finally,the area of the full-scale tracer experiment which alsocontains several sites of other special projects during theIOP (street canyon energetics, satellite ground truth) ismodeled using a very detailed physical scale-model in awind tunnel. In the present paper details of all theseactivities are presented together with first results.