St Andrews University, St. Andrews, KY16 9SS, UK

A review is given of our current understanding of the magnetohydrodynamics of solar flares. The theory of reconnection in 2D is now well understood, but in 3D we are only starting to understand the complexity of magnetic topology and the different ways in which reconnection may occur. Small flares may be driven by footpoint motions in emerging or interacting flux regions or they may occur at quasi-separatrix layers in complex regions. For large eruptive flares an MHD instability or catastrophe is thought to be responsible for the eruption which then drives reconnection above the flare loop systems. This model is supported by simulations and Yohkoh observations. Particle acceleration may occur by turbulent or direct electric fields at the reconnection site or in the different kinds of MHD shock wave that are associated with the flare process.