The significant changes in physics behaviour expected in low-aspect-ratio plasmas are outlined. Theses changes occur especially in the equilibrium, MHD stability, energy confinement and neo-classical effects. The START experiment has obtained the first observations of such plasmas at aspect ratios down to 1.3. The results are compared with the behaviour predicted by theory, simulation, and extension of empirical scalings. Two unexpected features of the START plasmas-the natural exhaust system and the freedom from major disruption-may offer significant advantages to the low-aspect-ratio 'spherical tokamak' reactor concept.