CCD-based X-ray detectors are getting to be used for X-ray diffraction studies especially in the studies where real time(automated)measurements and time-resolved measurements are required. Principles and designs of two typical types of CCD-based detectors are described; one is the system in which x-ray image intensifiers are coupled to maximize the detective quantum efficiency for time-resolved measurements, and the other is the system in which tapered optical fibers are coupled for the reduction of the image into the CCD, which is optimized for automated measurements for protein crystallography. These CCD-based X-ray detectors have image distortions and non-uniformity of response to be corrected by software. Correction schemes which we have developed are also described.