Brain-computer interfaces (BCIs) convert brain signals into outputs that communicate a user's intent. BCIs can be used by people to communicate and interact with their environment. However, the prevailing non-invasive and invasive sensor methods have important limitations. Electrocorticographic (ECoG) recordings from the surface of the brain could be a robust and high-fidelity alternative to existing sensor methods. This tutorial will provide an overview of the history of ECoG recordings; describe the types of signals present in ECoG and their relationship to signals detected using EEG and intracortical microelectrodes; and finally give examples of successful use of these signals in real time for BCI purposes and also for diagnosis.