The development of fusion energy has been a large-scale scientific undertaking of broad interest. The magnetic plasma containment in tokamaks and the laser-drive ignition of microfusion capsules appear to be scientifically feasible sources of energy. These concepts are bounded by questions of required intensity in magnetic field and plasma currents or in drive energy and, for both concepts, by issues of plasma stability and energy transport. The basic concept and the current scientific issues are described for magnetic fusion and for the interesting, but likely infeasible, muon-catalyzed fusion concept. Inertial fusion is mentioned, qualitatively, to complete the context. Fusion appears to release energy in rather large quantities (about 1000 MW) and significant new devices are needed to make progress. For magnetic fusion, the required net energy production within the plasma may be accomplished soon, but the more useful goal of self-sustained plasma ignition requires a new device of somewhat uncertain (factor of 2) cost and size.