It has recently become possible to record the EEG simultaneously with fMRI, providing whole-brain maps of the hemodynamic (fMRI) correlates of electrophysiological (EEG) activity. The combination of the EEG high temporal resolution with the fMRI high spatial resolution offers a unique opportunity for studying the spatio-temporal dynamics of brain activity noninvasively. Here, I will focus on the application of EEG-fMRI to the study of spontaneous epileptic activity in patients undergoing pre-surgical evaluation. The EEG is used to identify electrical discharges associated with epileptic seizures, as well as interictal epileptiform spikes, and the fMRI correlates of such EEG features can then be used to localize the brain networks involved in the epileptic activity. I will first introduce the basic principles and main challenges of the EEG-fMRI technique. I will then present results regarding the investigation of the link between EEG and fMRI signals, as well as the functional brain connectivity underlying seizure propagation. Appropriate biophysically-inspired models are employed in order to extract the relevant information from the EEG-fMRI data. It is shown that, in this way, important insights may be gained into the spatio-temporal dynamics of epileptic activity.