Although alternative, noninvasive methods are being developed, current research on rodent sleep still almost exclusively relies on recording the electroencephalogram (EEG). EEG provides information about the electrical activity of the brain and is, in combination with the electromyogram (EMG), primarily used to distinguish the different sleep and wake states. This unit describes the technique used to record EEG and EMG signals in freely moving mice, under standard laboratory conditions or specific experimental protocols such as sleep deprivation (SD). In addition to its use to determine behavioral state, the EEG contains a wealth of information concerning rhythmic brain activity that can be extracted using signal analysis tools. We will describe the protocol for implantation of EEG and EMG electrodes, provide examples of experimental designs, and discuss data acquisition and analysis illustrating the type of information that can be obtained from the EEG in mice. Curr. Protoc. Mouse Biol. 2:54-74 © 2012 by John Wiley & Sons, Inc.