The basic physical principles of magnetohydrodynamic generation are described and the electro-dynamics and thermodynamics discussed. The interaction is controlled by the plasma conductivity, which is low, and methods of increasing it are mentioned. The quasi-one-dimensional flow equations are presented and methods of solution outlined. The practical problems are discussed and a survey is made of experimental work to date. The immediate prospects for open cycle fossil fuel devices give grounds for cautious optimism and possible future developments include superconducting electromagnets, closed cycles for nuclear applications and a.c. generation.