An overlapping need exists between the climate research and the radiation protection communities to improve the metrology for atmospheric radon concentration and radon flux measurements. The EMPIR project 19ENV01 traceRadon works toward these goals for the benefit of both large scientific communities by providing the necessary infrastructure for measuring these aforementioned variables. In addition, it will generate data at four selected European sites for validation of radon flux models and inventories and will create the first standard protocol for applying the radon tracer method (RTM). The special issue aims to collect the direct and indirect outcomes of the traceRadon project. It includes papers presenting results of the laboratory and field campaigns carried out within the project.