Brain-computer interfaces (BCIs) are a promising technology intended for the treatment of diseases and trauma of the nervous system. BCIs establish a direct connection between the brain areas that remain functional and assistive devices, such as powered prostheses and orthoses for the arms and legs, motorized wheelchairs, artificial sensory organs and other technologies for restoration of motor and sensory functions. BCIs of various kinds are currently developing very rapidly, aided by the progress in computer science, robotic applications, neurophysiological techniques for recording brain activity and mathematical methods for decoding neural information. BCIs are often classified as motor BCIs (the ones that reproduce movements), sensory BCIs (the ones that evoke sensations), sensorimotor BCIs (the ones that simultaneously handle motor and sensory functions), and cognitive BCIs intended to regulate the higher brain functions. All these BCI classes can be either invasive (i. e. penetrating the body and/or the brain) or noninvasive (i.e. making no o little contact with the body surface). Noninvasive BCI are safe to use and easy to implement, but they suffer from signal attenuation by scalp and skin, its contamination with noise and artifacts, and an overall low information transfer rate. Invasive BCIs are potentially more powerful because they utilize implanted grids that can both record neural signals in high-resolution and apply stimulation to the nervous tissue locally to deliver information back to the brain. BCI technologies are being developed not only for individual use, but also for collective tasks performed by multiple interconnected brains.