Much of our attention as electroencephalographers is devoted to the identification and localization of spikes and seizures. Atlases, primers, and texts of electroencephalogram (EEG) interpretation provide a wealth of information to guide seizure identification, but often the diagnosis is based on the same principle as Justice Potter Stewart’s maxim for identifying obscenity in Jacobellis v. Ohio: “I know it when I see it.”1 Virtually all of the mathematical seizure detection algorithms currently in use are based on empiric observations of EEG activity that occurs contemporaneously with behavioral seizures, or resembles the electrical activity we see during such behaviors. Ideally, we should be able to derive the parameters for identifying electrographic seizures from a detailed understanding of the underlying neuronal pathophysiology that generates abnormal rhythmic activity, disrupting normal brain circuit functions and behaviors. Unfortunately, we are not there yet. In many cases, however, we have at least a rudimentary knowledge of the neurons and brain structures involved in seizure generation. This chapter will review what we know about how seizures are generated and how that translates into the patterns we observe in EEG recordings.