A large solar flare is thought to occur when a sheared magnetic arcade loses equilibrium or goes unstable and erupts, and drives magnetic reconnection in the stretched-out magnetic field lines. These two key processes of magnetic eruption and magnetic energy conversion by reconnection are reviewed briefly, with an account of recent analytical and numerical models. When the height or length of a prominence in a sheared coronal arcade is too great it may erupt and drive the formation and reconnection of a current sheet below it. Recent progress in fast steady-state reconnection theory has explained many puzzling features of numerical experiments, and has shown how a new process of magnetic flipping can reconnect fields in three dimensions. Also numerical modelling of the formation of flare loops and ribbons by reconnection has accounted for many observational properties.