This chapter describes the sources of radioactive and non-radioactive contamination in the Arctic and Nordic Seas. The primary and secondary sources of radioactivity in the study region are enumerated and described in Section 1.1. Section 1.2 focuses on a detailed description of three major Russian nuclear industries: (1) the Mayak Production Association, Chelyabinsk; (2) the Siberian Chemical Combine, Tomsk-7; and (3) the Mining and Chemical Combine, Krasnoyarsk-26. Section 1.3 provides a substantial description of non-radioactive pollution, including its sources and spread in the marine environment of the Barents, White, Kara, and Laptev Seas. The descriptions given here have been prepared from information from a range of open-literature material, including a wealth of Russian material and more widely known publications; for example, Arctic Monitoring and Assessment Program (AMAP) reports. An effort has been made to provide the most recent information, although the ever-changing status of pollution sources challenges an evaluation of the present situation.