Decontamination plays an important role in ensuring the safe and long term operation of nuclear power plants. Therefore nuclear power plant operators continuously adopt new decontamination techniques or improve existing decontamination processes to reduce radiation exposures encountered during normal operation, shutdowns, and maintenance and inspection activities during subsequent plant operation. These activities have resulted in a large amount of information which is reflected in this publication. Experiences, lessons identified and good practices for decontamination during outage in nuclear power plants in operation are described. The goal was to consolidate, update, reorganize and expand upon information contained in other IAEA publications related to the subject. The result is a state-of-the-art reference for Member States to help select decontamination techniques suitable for their specific needs.