Sleep has been a subject of enquiry for millennia, since the earliest Greek philosphers and scientists. But early writings on the subject amounted to little more than mere conjecture, and in terms of scientific understanding, the mechanisms of sleep remained largely mysterious until the advances of the mid-20th Century. Since then, our understanding has progressed in leaps and bounds, although there still remains some work to be done.
Below is a chronological timeline of the major landmarks in sleep research. It is necessarily a subjective list, and it owes a debt of gratitude to the Harvard Medical School Division of Sleep Medicine's interactive website: "Sleep: A Historical Perspective" (http://healthysleep.med.harvard.edu/interactive/timeline).