The fundamental elements of video-polysomnography are suggested by its name: video (watching patients and their body movements) polysomnography (recording the state of wakefulness or the different stages of sleep). Nowadays, digital polysomnographic recording systems can allow the video to be modified off-line to enlarge patient's details, select the most important polysomnographic parameters and allow modification of the amplitude with appropriate filter settings and also to modify the EEG derivations. Polysomnographic technician performs several tasks during overnight recording: supervision of the recording to ensure perfect functioning of electrodes and transducers; integration of the recording with additional electrodes if new events occur during night; intervention during an event to prevent injury to the patient; intervention during the recording to verify space and time orientation in the patient; and intervention during recording to question the patient about the event.