[en] An accident in which the normal core cooling is lost could lead to fuel elements melting and fission product release beyond the plant limits. Nuclear power plants are designed with engineering systems and associated operational procedures which provide an in-depth defence against such accidents. Iodine is a major contributor to the potential source term to the environment, thus a good understanding of its behaviour and validated calculation tools are required to perform meaningful risk analyses and make decisions in the field of accident management, mitigation measures and emergency procedures. A number of experimental programmes, involving separate-effect and integral tests have been carried out during the last decade, providing new and valuable results that have improved our understanding of iodine phenomena. A modelling effort has also been pursued in order to encapsulate the acquired knowledge in the calculation tools prepared for predicting the iodine behaviour under severe accident conditions. In view of the progress made, the Working Group on Analysis and Management of Accidents (GAMA) considered the necessity of producing a status paper on iodine chemistry, with the following objectives: - to review insights gained and evaluate the progress made during the last 10 years on the understanding of phenomena governing iodine chemistry and release in the case of a reactor severe accident, - to evaluate the current status of iodine chemistry knowledge and tools used for source term prediction in connection with accident management and emergency planning, under various reactor conditions, to identify the remaining weaknesses, discuss the reactor safety relevance of these issues and make recommendations as necessary. This paper aims at shedding light on the present situation, helping end-users and decision makers to adequately address questions related to iodine behaviour under severe accident conditions, and to essential programmes of work in this area