Fusion energy science promises a virtually limitless supply of clean energy for mankind’s growing needs. To reach fusion conditions, the gaseous fuel needs to be heated to temperatures of hundreds of millions of degrees and this mixture needs to be confi ned for a long enough time for fusion reactions to occur. One approach is to develop a magnetic “bottle,” in which the ionized gaseous fuel (called a plasma) is held in place by magnetic fi elds. The tokamak is the most successful such device thus far, with its doughnut shaped toroidal chamber. In this device, the plasma is confi ned by magnetic fi elds produced both by external axisymmetric coils and by current fl owing in the plasma itself. The plasma current is usually driven by a transformer, necessitating the periodic shutdown and restart of the device. Current research is underway to develop techniques allowing continuous operation of the tokamak at high plasma pressure and improved effi ciency. Progress in tokamak research is reviewed, including a discussion of the most recent advances in understanding the physical processes governing the plasma’s behavior. Large and small scale instabilities can affect plasma performance in many ways. Much of the research on tokamaks has focused on the prediction, measurement and control of these instabilities. Sophisticated numerical models have advanced rapidly in recent years and are now capable of reproducing, and even predicting, much of the behavior of the tokamak plasma. This progress has brought us to the point where we are preparing for the construction of the International Thermonuclear Experimental Reactor (ITER), which is expected to produce hundreds of megawatts of fusion power using the deuterium-tritium fusion reaction.