In the recent years, the role of imaging in radiation therapy has expanded considerably, evolving from being mostly used to help delineate structures for treatment planning to being an indispensable daily tool for the verification of patient localization and sometimes, treatment plan adaptation. Along with the excitement the new technology brought, came a new set of challenges for the professionals involved in the process, ranging from understanding basic imaging and image registration concepts, to providing quality assurance checks for equipment involved and ensuring congruence between imaging and treatment beams, to understanding when and where to use what imaging option in order to achieve the most clinically while minimizing workload and radiation doses. This panel will provide an up-to-date review of the current practice, from technology to clinical protocols. At the conclusion of this activity, the learner will be able to do the following: 1. Describe kV and MV linac-based imaging systems and their basic imaging characteristics and performance, be familiar with the appropriate quality assurance requirements, and have knowledge of the imaging doses involved. 2. Explain the principles and the role of image registration in patient localization and plan adaptation, have knowledge of the various image registration algorithms (thin spline, B-spline, demons, elastic etc.), distinguish between 2D/3D, single/multi-modality imaging. 3. Quantify the absolute and relative accuracy of various imaging systems and have general guidelines outlining the use of imaging as an aid for more accurate radiation delivery.