This document provides an overview of brain-computer interfaces (BCI). It discusses the history and development of BCI, including early work using electrodes implanted in monkeys. The document describes different approaches to BCI, such as invasive, semi-invasive, and non-invasive methods. Applications mentioned include providing communication assistance to disabled individuals, controlling devices like wheelchairs, and monitoring brain activity for various purposes. Current BCI projects highlighted are BrainGate, BCI2000, and using BCI to control robots. The conclusion discusses BCI as a promising emerging technology with potential therapeutic applications.