This paper presents an overview of the state of the art of core transport studies in JET. It covers in various sections the topics of heat transport, particle and impurity transport, momentum transport, internal transport barrier physics and integrated core and edge modeling. For each topic, a brief summary of older results obtained under the JET Joint Undertaking and a review of recent results obtained under the European Fusion Development Agreement are presented and discussed in view of the possibility of extrapolating to ITER plasmas. A final outlook of future developments of core transport studies in JET concludes the paper.