The overall objective of FAIR CT.96.1394 (1997-99) was to achieve improvements in the methodology of fish tagging techniques with emphasis on applications in fisheries research and stock assessment. The report consists of ten chapters. The first three are essentially introductory, sketching the background and concerns that led to the Concerted Action, and describing its rationale and objectives. Chapters 4 to 8 address the various objectives of the project, whilst Chapters 9 to 11 provide a conclusion and additional information. Chapters 4 to 8 are based on the deliberations of four separate working groups, which tackled different aspects of the subject and then presented their conclusions for debate in a plenary session. Chapter 4 is devoted to conventional identification tags and tagging techniques. The content is comprehensive, but not exhaustive, because this area has been reviewed before. Responsible for this chapter were: Mr. Curt Insulander, (SRI, Sweden), Dr Josianne Støttrup (DIFR, Hirtshals), Mr Stig S. Pedersen (DIFR, Silkeborg) and Mr. Vilhjalmur Thorsteinsson (MRI, Reykjavik). Chapter 5 is concerned with electronic tags and provides the most up-to-date compilation of the field, covering tag function, engineering and methodology in some detail. This chapter provides the technical core of the report.