Fusion faces three types of challenge: scientific, economic, and environmental. Many scientists believe that both inertial and magnetic fusion can meet the scientific challenge in the sense that they can produce net energy. The National Ignition Facility is expected to demonstrate ignition of an inertially confined plasma within a decade. The economic and environmental challenges will remain. This paper describes research on ion beam inertial fusion. Ion accelerators are, in many ways, ideally suited to the requirements of fusion power production. They can be durable, reliable, and efficient. They can easily achieve the required pulse repetition rates. Cost and beam quality are the principal issues. The cost of a fusion accelerator, if it were built with today's technology, would be acceptable for large power plants (several gigawatt electric). Cost reductions that will allow good economics at smaller plants appear possible. The environmental issue is activation produced by neutrons from deuterium–tritium fuel. For ion beam fusion, it appears possible to shield the structure of the fusion chamber with a neutronically thick liquid layer. This method of protection greatly relaxes the requirements on materials and endows deuterium–tritium fusion systems with many of the advantages of advanced, aneutronic fusion systems. The inertial fusion community in the United States has recently proposed a new programme for the development of inertial fusion as a commercial energy source. This paper gives a brief description of the proposed programme.