In spite of the advance of noninvasive localizing methods in the presurgical evaluation of focal epilepsies, invasive EEG is still frequently indicated in a substantial subset of patients. This strongly depends on the site and extension of the suspected epileptic generator, as well as the nature and location of the underlying lesion, if any. In this context, SEEG is increasingly used since it provides a 3D assessment of the epileptogenic network, appears safe and effective, and enables a therapeutic option (radio-frequency thermocoagulation). Whether SEEG will change the decision based on noninvasive data, whether it is likely to find a focal resectable epileptogenic zone, and whether hypotheses are strong enough to design a coherent electrode implantation scheme are crucial issues before proceeding, given the spatial sampling limitation inherent to the method. SEEG interpretation then relies on a careful analysis of interictal slow waves (lesional zone), interictal paroxysmal activities (irritative zone), and seizure discharges (epileptogenic zone) to evaluate their causal relationship and to allow—through their 3D representation—a careful individualized planning of the surgical resection. This process necessitates a significant multidisciplinary expertise and careful coordination among specialists, with the full patient/family’s empowerment to participate in the team’s decision.