On the surface, epilepsy seems like an easy diagnosis to make—how could anyone miss a major event like a seizure? However, epilepsy can be deceiving. There are many types of seizures that are more subtle than the obvious tonic-clonic seizure, and many seizure types that look bizarre are misdiagnosed as nonepileptic. As a result, a large number of people with epilepsy experience lengthy delays before appropriate diagnosis and therapy provide relief. Conversely, there are many nonepileptic events that are easily mistaken for seizures, which lead to numerous misdiagnoses of epilepsy in nonepileptic patients. These patients are subjected to unnecessary treatment with toxic medications. In this article, I examine the range of diagnostic tests that can be used to establish a diagnosis of epilepsy, to help select the most appropriate form of therapy, to monitor and adjust therapy, to select appropriate surgical candidates, and to decide when therapy can be discontinued.