Abstract: Image-guided radiotherapy (IGRT) combines scanning and radiation equipment, providing images of pa-tients'organs during treatment and improving the accuracy and precision of radiotherapy. Adaptive radiother-apy (ART), the next step in image-guided radiotherapy, is an emerging radiation treatment with an increasedprobability of tumor control and reduced or equivalent toxicities. Adaptive radiation therapy was developed tocompensate for setup error and organ motion. The treatment plan can be modified by a systematic feedbackof measurements. The adaptations can be based upon simple alterations in the geometric placement, shapeof the target, normal structures or the target's biological changes (e.g. metabolism, hypoxia, perfusion andreplication) as the treatment is delivered. In this process, field margin and treatment dose can be routinely cus-tomized to each individual patient to achieve a safe dose escalation. ART is a promising technique that en-ables individualized dynamic treatment planning. In this article, we summarize the recent advances in im-age-guided adaptive radiation therapy. We introduce some related concepts and approaches in an effort toprovide a comprehensive understanding of the emerging clinical image-guided adaptive radiation therapytechnologies.