Consciousness is a central concept in epileptology, relevant to the understanding of both focal and generalized seizures. Within focal seizures, impairment of consciousness has long been considered as the main criterion differentiating complex partial seizures (CPS) from simple partial seizures With the development of improved tools for investigating human brain function, new insights into the brain mechanisms of altered consciousness in CPS have become available. This paper reviews the existing literature on how the currently available methods can be used to address the fundamental issue of how CPS alter consciousness.