Characterization of a contaminated site is an essential step before embarking on a programme for environmental remediation. It is not only necessary for assessing the associated radiation risks but also important to support the required project design, planning and cost estimate.This webinar is intended to present and discuss updated approaches and methodologies applicable for determining the characteristics of radioactively contaminated sites, remaining challenges and needed innovations. Four main areas will be addressed:(i) characterization of sites with buried wastes,(ii) groundwater characterization,(iii) sites contaminated with mining and processing wastes and(iv) data visualization and interpretation.The webinar will also showcase activities of the IAEA in this field including the Mobile Unit for Site Characterization.