With the whole-cell mode of patch-clamp the membrane current is recorded from a cell under the voltage-clamp. The membrane potential response of a cell is also measured and manipulated under a current-clamp. The method enables one to correlate the macroscopic aspects of ion channels with their microscopic properties. It also demonstrates how these ion channels regulate the membrane potential. This chapter summarizes the basic concepts of whole-cell patch-clamp recording and the practical procedures and protocols used to examine currents through channels/transporters across entire cells.