Type I X-ray bursts are thermonuclear flashes observed from accreting neutron stars in binary star systems. Due to the strong gravity and high temperature, these bursts probe nuclear physics and reactions not encountered elsewhere in nature, and also depend on the properties of the underlying neutron star – and hence the properties of matter at these extreme conditions. The ultimate goal of this project is to reconcile, in detail, experimental, observational and numerical investigations on these bursts and the nuclear reactions that power them. To achieve this goal, we have assembled a team to identify the key nuclear reactions which influence the burst lightcurve; take advantage of new rare-isotope accelerator- based experiments and satellite observations to provide stringent tests of numerical models; identify specific cases of ignition and burning from observation-model comparisons; and provide qualitatively new constraints on the properties of neutron stars and nuclear matter.