The course offers a broad and comprehensive overview of radiological characterisation in the decommissioning process. It covers key elements such as characterization requirements, historical site assessment, characterization planning, activation calculations, survey techniques, instrumentation for in-situ measurements, use of scaling factors, characterization data collection, analysis and reporting. The course also covers quality management, health and safety aspects related to characterization activities. It consists of 11 modules of average 10-15 min each and is targeting newcomers and advanced professionals with technical roles. By the end of this course, learners will be prepared to take a more hands-on approach to the topic.