The development and clinical use of conformal radiation therapy, and the application of modern computer-controlled radiation therapy treatment techniques to the delivery of conformal therapy, has been a major research area in the field of radiation oncology in recent years. The introduction of three-dimensional (3-D) patient imaging, 3-D treatment planning systems, computer-controlled treatment machines equipped with multileaf collimators, and the continuing increase in computer power and software sophistication has finally allowed the clinical implementation of the kinds of conformal treatment planning and delivery that were envisioned decades ago. The use of 3-D treatment planning in conjunction with conformal treatments and the analysis of clinical normal tissue complications has also begun to give the field the clinical complication (and eventually tumor control) probability data which can be used to truly optimize radiation treatments. At this centennial anniversary of the discovery of the x ray, it is appropriate to look back at the contributions which have led to the current developments in conformal therapy. Few if any of the "new developments" associated with modern computer-controlled conformal therapy (CCRT) are actually new. However, modern technology has finally progressed to the point that we can integrate all of the features that are necessary to really make the concepts work in the clinic. This paper traces some of the developments which have led to the current interest and progress in CCRT treatments. A brief summary of the current status of conformal therapy and the work still to be done is also included.