A refrigerator equipped with a door that becomes transparent as necessary to make the interior thereof visible is disclosed. The refrigerator includes a cabinet having a storage compartment defined therein, a lighting device for illuminating the interior of the storage compartment, a door, which is hingedly coupled to the cabinet to open and close the storage compartment, and has an opening and a panel assembly including a front panel disposed on the front surface thereof, a sensor for detecting sound waves, which are generated by a knock input applied to the door and are transmitted through the front panel, and a controller for controlling the lighting device to allow light to be transmitted through the panel assembly, thus making the storage compartment visible from outside the door through the opening when a predetermined knock input is detected.