IntroductionSleep disorders are known as conditions that have a huge impact on the quantity and quality of a person's sleep. They are common in the general adult population, as the prevalence of sleep disorders increases as the population ages. Sleep disorders are a problem that most people suffer from as they age. Many decades ago, sleep disorders were known to people and doctors. Classification of sleep disorders is necessary to discriminate between disorders and facilitate understanding of symptoms, etiology, and pathophysiology that allows for appropriate treatment (Michael, 2012). The International Classification of Sleep Disorders (ICSD) is an authoritative clinical text for the diagnosis of sleep disorders. The ICSD book is under revision due to many reasons that could have caused the patient's sleep disturbance. The previous version of the book mainly focused on the main symptoms (insomnia, excessive sleepiness, and abnormal events occurring during sleep), but they were not based on pathophysiology because most cases of sleep disorders were still unknown. The purpose of this article is to review the differences between symptoms and pathophysiology. As well as critically appraise the scientific evidence on ICSD that could trigger awareness of the general public's views on the importance of sleep. LiteratureA Journal Search The PubMed literature search was performed using the heading “Classification of Sleep Disorders.” The resulting articles were filtered for related words. The topics were explored in depth by reading the abstract. Most of the references cited from that article have been checked to be in the correct form. The Michael J. Thorpy quote has been checked for a new article...... half of the article...... profound disorder is impressive and has demonstrated many benefits that would help the doctor to be more accurately determine information about the patient's sleep disorders. Summary and Conclusion The literature in this area is vast and challenges today's medical technology. Studying and learning new symptoms for sleep disorders is as difficult as the brain exam where the doctor has to find out how the brain works while we sleep. Various disorders have been classified, but there are many others that still remain unknown to the world. This literature provides knowledge of something we thought so simple, but yet is very complicated in ways that require more than future knowledge. The author has covered most of the important symptoms of the disorders. The ICSD is currently being revised and updated to provide a more accurate diagnosis if someone is suffering from a sleep disorder.