Most seizures in critical ill patients are non-convulsive, and some patients may develop non-convulsive status epilepticus (NCSE), a state of continuous or repetitive seizures without convulsions. With the growing use of continuous electroencephalogram (EEG) monitoring in neuro-intensive care units, non-convulsive seizure (NCS) and NCSE are increasingly diagnosed in patients with impaired consciousness, and progress has been made in identifying various EEG characteristics of NCS/NCSE. Epidemiological studies have contributed to a better understanding of etiologies and risk factors for NCS and NCSE. However, sufficient clinical trials about the treatment of NCS and NCSE are still lacking. The appropriate level of aggressiveness in the treatment of NCSE is still debated, particularly with regard to the use of anesthetics in patients with refractory NCSE. In this review, we summarize the EEG, clinical, epidemiological, diagnostic and therapeutic knowledge of NCS and NCSE in the neuro-intensive care setting in detail.