•Gene editing using CRIPSR/Cas has the potential to increase anti-tumor efficacy and persistence of adoptively transferred cells.•Allogeneic T cells can be made safer and more effective using multiplex genome editing and are already in the clinic.•Base editing and prime editing are promising approaches for advanced T cell engineering but need further optimization of editing efficiency. T cells engineered to express transgenes such as chimeric antigen receptors (CAR) or modified T cell receptors (TCR) represent a new pillar of cancer therapy. Use of CRISPR/Cas gene–editing tools now allows even stronger and more precise control over the fate and function of engineered T cell therapies, including multiplex genome editing to facilitate use of off-the-shelf allogeneic T cells and novel approaches which have the potential to overcome some of the limitations of canonical Cas9-mediated DNA cleavage. This review summarizes the CRISPR/Cas techniques that have been used in preclinical research and outlines those that currently being tested in clinical trials.