During the last few years the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR)a has undertaken a broad review of the sources arid effects of iol~izir~g radiation Nine scientific annexes on particular sabjects were issued in the UNSCEAR 1993 Repon Two fudler annexes have been completed, and these comprke UIC UNSCEAR 1994 Report. This is the twelfth substantive Report of the Committee, informing the General Assenlbly and the scicntific and world conlnlunity of its latest assessmentsb. The two reports, 1993 and 1994, are complementary and provide a coherent summary of the Committee's findings and programme of work