On July 14, 2011, the FDA issued draft guidance entitled “In Vitro Companion Diagnostic Devices.” The guidance is intended to assist sponsors planning to develop a therapeutic product that depends on the use of an in vitro companion diagnostic device for its safe and effective use or an in vitro diagnostic device that is intended for use with a corresponding therapeutic product and included in the instructions for use in the labeling of those products. The guidance defines in vitro companion diagnostic devices; explains the need for FDA oversight of companion diagnostic devices; clarifies that, in most circumstances, if use of a companion diagnostic device is essential for the safe and effective use of a therapeutic product, the diagnostic device and therapeutic product should be approved or cleared contemporaneously by FDA for the use indicated in the therapeutic product labeling; provides guidance for industry and FDA staff on possible premarket regulatory pathways and FDA’s regulatory enforcement policy; and describes certain statutory and regulatory approval requirements relevant to therapeutic product labeling that stipulate concomitant use of a companion diagnostic device to ensure safety and effectiveness of the therapeutic product. Comments on the guidance are due by September 12, 2011.