A new generation high field spherical tokamak, ST40, is currently under construction at Tokamak Energy Ltd (TE). The main parameters of ST40 are: R 0 =0.4-0.6m, A =1.7-2.0, I pl =2MA, B t =3T, κ =2.5. It will have power supplies based on ultracapacitors, liquid nitrogen-cooled copper magnets, up to 2MW of neutral beam injected (NBI) power, and a pulse length of ∼3s when operating at full power. To stabilize the highly elongated plasma, in addition to active vertical control, liquid nitrogen-cooled passive plates will be installed. ST40 is aimed at demonstrating burning plasma condition parameters (nTτ E) and may also be suitable for DT operations in future. The main physics and engineering challenges are caused by the high toroidal field, relatively high plasma current, and wall and divertor power loads.