Proper heat removal from the fuel is essential for the safe operation of nuclear reactors used for electricity production. As nuclear fuel is burnt it undergoes important changes, including a degradation of its thermal conductivity. This important phenomenon needs to be reliably predicted in order to make better use of the fuel, a factor which can help to achieve the economic competitiveness required by today's markets. This report communicates the results of an international seminar which reviewed recent progress in the field of nuclear fuel thermal conductivity and sought to improve the models used in computer codes predicting thermal performance. State-of-the-art knowledge is presented for both uranium-oxide and mixed-oxide fuels loaded in water reactors.