This book presents the Neuroprocessor, a novel computational neuronal interface device implemented in VLSI technology. In addition to neuronal signals acquisition, it can process the data, generate stimuli and transmit the data over wireless channels, while using minimum electric energy. The NeuroProcessor opens with a brief background on neuronal communication and microelectrode recording. It introduces three generations of the Neuroprocessor and presents their architecture, circuits and algorithms. Applications to a miniature head-stage for in-vivo experiments and multi-electrode arrays for in-vitro studies are described.