Abstract. The National Spherical Torus Experiment is a medium-sized device whose mission includes the evaluation of confinement and stability at low aspect ratio. This paper will discuss various characteristics of NSTX H-mode discharges, including transport, scaling of the threshold power, macroscopic stability and investigations of the H-mode edge region with probes and spectroscopic imaging diagnostics. In summary, both ELM-free and ELMy H-modes have been triggered on NSTX, with either neutral beam or radio-frequency auxiliary heating. Energy confinement time as high as 120 ms was obtained transiently in ELM-free H-mode, which is 50% above the ITER98 Hpby(2) scaling. Both giant and ``grassy'' ELMs have been observed. Wall conditioning has been found to play a pivotal role in obtaining good H-mode discharges. Access to H-mode was first enabled by boronization of the plasma facing components. The first long pulse H-modes were obtained after a 350 deg. C bakeout of the plasma facing components, followed by boronization. A reduction in the intrinsic non-axisymmetric error field has helped to extend the duration of the H-mode phase by reducing the occurrence of locked modes.