The prediction of the radiation dose to man as a result of food chain exposure to tritium requires a knowledge of the tritium uptake and retention in plants. The tritium behaviour in vegetation is very different from that of most other radionuclides and its transfer modelling must be based on specific transfer data. The uptake depends primarily on the chemical form of tritium in the plant environment. Early studies on tritium transfer to plants were focussed on the mechanisms by which tritium oxide (HTO) can enter the plants, and participate in water and hydrogen cycles. Interest has now shifted to investigations of the transfer of elemental tritium (HT or T2) and tritiated carbon compounds. While the transport and incorporation of tritium as HTO is well documented, the processes of HT transfer to vegetation are not well understood. This paper reviews the current status of our knowledge on the transfer of different tritium forms to tissue water and organic constituents of plants.