Gamma delta (γδ) T cells are non-conventional T lymphocyte effectors that can interact with and eradicate tumour cells. Several data demonstrate that these T cells, which are implicated in the first line of defence against pathogens, have anti-tumour activity against many cancers and suggest that γδ T cell-mediated immunotherapy is feasible and might induce objective tumour responses. Due to the importance of γδ T lymphocytes in the induction and control of immunity, a complete understanding of their biology is crucial for the development of a potent cancer immunotherapy. This review discusses recent advances in γδ T basic research and data from clinical trials on the use of γδ T cells in the treatment of different cancers. It analyses how this knowledge might be applied to develop new strategies for the clinical manipulation and the potentiation of γδ T lymphocyte activity in cancer immunotherapy.