Recent advances in tokamak research have led to an improved understanding of the plasma requirements for achieving long pulse ignited burn in a tokamak plasma. This paper presents an assessment of these requirements in the areas of plasma energy confinement, plasma stability at high beta-values, plasma heating, particle and impurity control, and non-inductive current drive. In all areas, the physics basis appears adequate to support a near-term demonstration of a fusion reactor core — a long-pulse ignition experiment — in a device of acceptable overall size and cost.