This course reviews the characterization of excessive sleepiness and the most common cause of sleepiness. Excessive sleepiness and resultant impaired alertness has been implicated to threaten the safety of others. The assessment of sleepiness is important for effective assessment and management of a patient with sleep dysfunction. Careful review of the Multiple Sleep Latency Test (MSLT) and the Maintenance of Wakefulness Test (MWT) will be correlated to the objective measurement of sleepiness and alertness as supported by regulatory agencies. The AASM Practice Parameters for Clinical Use of the MSLT and MWT are reviewed.