Hans Berger (21 May 1873 – 1 June 1941) was a German psychiatrist. He is best known as the inventor of electroencephalography (EEG) in 1924, which is a method used for recording the electrical activity of the brain, commonly described in terms of brainwaves, and as the discoverer of the alpha wave rhythm which is a type of brainwave.Alpha waves have been eponymously referred to as the "Berger wave."

Berger was born in Neuses (now part of Coburg), Saxe-Coburg and Gotha, Germany.

After attending Casimirianum, where he gained his abitur in 1892, Berger enrolled as a mathematics student at the Friedrich Schiller University of Jena with the intention of becoming an astronomer. After one semester, he abandoned his studies and enlisted for a year of service in the cavalry. During a training exercise, his horse suddenly reared, and he landed in the path of a horse-drawn cannon. The driver of the artillery battery halted the horses in time, leaving the young Berger shaken but with no serious injuries. His sister, at home many kilometres away, had a feeling he was in danger and insisted their father telegram him. The incident made such an impression on Berger that, years later in 1940, he wrote: "It was a case of spontaneous telepathy in which at a time of mortal danger, and as I contemplated certain death, I transmitted my thoughts, while my sister, who was particularly close to me, acted as the receiver."

On completion of his military service, and obsessed by the idea of how his mind could have carried a signal to his sister, Berger returned to Jena to study medicine with the goal of discovering the physiological basis of "psychic energy." His central theme became "the search for the correlation between objective activity in the brain and subjective psychic phenomena."

After obtaining his medical degree from Jena in 1897, Berger joined the staff of Otto Ludwig Binswanger (1852–1929), who held the chair in psychiatry and neurology at the Jena clinic. Habilitated in 1901, he qualified as a senior university lecturer in 1906 and physician-in-chief in 1912, eventually succeeding Binswanger in 1919. He also collaborated with two famous scientists and physicians, Oskar Vogt (1870–1959) and Korbinian Brodmann (1868–1918), in their research on lateralization of brain function. Berger married his technical assistant, Baroness Ursula von Bülow, in 1911 and later served as an army psychiatrist on the Western front during World War I. He was elected Rector of Jena University in 1927.

In 1924, Berger succeeded in recording the first human electroencephalogram (EEG), a term he coined. Filled with doubt, he took five years to publish his first paper in 1929, which demonstrated the technique for "recording the electrical activity of the human brain from the surface of the head." His findings were met with incredulity and derision by the German medical and scientific establishments. Having visited the EEG laboratory at Jena in 1935, American roboticist William Grey Walter noted that Berger:

... was not regarded by his associates as in the front rank of German psychiatrists, having rather the reputation of being a crank. He seemed to me to be a modest and dignified person, full of good humour, and as unperturbed by lack of recognition as he was later by the fame it eventually brought upon him. But he had one fatal weakness: he was completely ignorant of the technical and physical basis of his method. He knew nothing about mechanics or electricity.

After British electrophysiologists Edgar Douglas Adrian and B. H. C. Matthews confirmed Berger's basic observations in 1934, the importance of his discoveries in electroencephalography (EEG) was finally recognized at an international forum in 1937. By 1938, electroencephalography had gained widespread recognition by eminent researchers in the field, leading to its practical use in diagnosis in the United States, England, and France.