In this paper we describe the hand of the humanoid iCub, an open source robotic platform funded by the European Commission. The principal design rationale was the necessity to supply the robot with sufficiently dexterous and sensorized hands in order to study complex skills such as manipulation. The final design has 9 actuators for each hand, 12 tactile sensors at each fingertip, 48 pressure sensors in the palm and 17 position sensors. The electronics for the sensors are embedded in the hand. As a preliminary application we tested the hand in a simplified grasping scenario in order to quantitatively evaluate the reliability and repeatability of the overall system.