Radiation therapy treatment planning and delivery capabilities have changed dramatically since the introduction of three-dimensional treatment planning in the 1980s and continue to change in response to the implementation of new technologies. CT simulation and three-dimensional radiation treatment planning systems have become the standard of practice in clinics around the world. Medical accelerator manufacturers have employed advanced computer technology to produce treatment planning/delivery systems capable of precise shaping of dose distributions via computer-controlled multileaf collimators, in which the beam fluence is varied optimally to achieve the plan prescription. This mode of therapy is referred to as intensity-mod ulated radiation therapy (IMRT), and is capable of generating extremely conformal dose distributions including concave isodose volumes that provide conformal target volume coverage and avoidance of specific sensitive normal structures. IMRT is rapidly being implemented in clinics throughout the USA. This increasing use of IMRT has focused attention on the need to better account for both intrafraction and interfraction spatial uncertainties, which has helped spur the development of treatment machines with integrated planar and volumetric advanced imaging capabilities. In addition, advances in both anatomical and functional imaging provide improved ability to define the tumor volumes. Advances in all these technologies are occurring at a record pace and again pushing the cutting-edge frontiers of radiation oncology from IMRT to what is now referred to as image-guided IMRT, or simply image-guided radiation therapy (IGRT). A brief overview is presented of these latest advancements in conformal treatment planning and treatment delivery.