Radiation therapy treatment planning and delivery capabilities have changed dramatically over the past decade and are in the process of changing even more dramatically over the next few years. Three-dimensional radiation treatment planning systems, once the purview of university research groups, are now commercially available and are rapidly being implemented in clinics around the world. These developments have prompted medical accelerator manufacturers to use advanced computer technology to produce treatment delivery systems capable of precise shaping of dose distributions via computer-controlled multileaf collimators (MLC). The latest development exploits the use of fields in which the beam intensity is varied optimally within the portal boundary and is referred to it as intensity modulated radiation therapy. This approach is capable of generating extremely conformal dose distributions including concave isodose volumes that provide specific avoidance of sensitive normal structures within complex treatment geometries. These new capabilities change the kinds of treatments that are possible, and that changes the process with which treatment planning and treatment delivery are performed. These technological advances show significant potential for improving both the quality of radiation therapy and/or improving the efficiency with which radiation therapy can be planned and delivered.