This report presents the views of the IAEA's International Nuclear Safety Advisory Group INSAG on the source term issue for LWRs of existing designs. The report considers the present status of source term research and analysis and their implications. It identifies problems which remain to be resolved and indicates areas where work should be initiated to improve safety. Contents: Introduction; Purpose; Probabilistic safety analysis; General issues; High source term sequences; Early containment failure; Remobilization of fission products; Bypass of containment; Other issues; Reduction of risk and source term through accident prevention, management and mitigation; Conclusions; Bibliography; Appendix: Implications of the source term from the Chernobyl accident.