thumb|right|220px|Reil's tomb on the Reilberg in [[Halle, Saxony-Anhalt|Halle (Saale), Germany, today Bergzoo Halle]]
Johann Christian Reil (20 February 1759 – 22 November 1813) was a German physician, physiologist, anatomist, and psychiatrist. He coined the term psychiatry – Psychiatrie in German – in 1808.
Reil was one of five children, and was the son of a Lutheran pastor in Northwest Germany. He married Johanna Wilhelmine Leveaux in October, 1788. Together they had two sons and four daughters.
Medical conditions and anatomical features named after him include Reil's finger (later called digitus mortuus or Raynaud syndrome) and the Islands of Reil in the cerebral cortex. In 1809, he was the first to describe the white fibre tract now called the arcuate fasciculus. He is frequently and erroneously credited with discovering the locus coeruleus, which was first described by Félix Vicq-d'Azyr.
Between 1779 and 1780, Reil became acquainted with the scientist Johann Friedrich Blumenbach while Reil was studying medicine in Göttingen. From 1788 to 1810, Reil worked in a hospital in Halle, Germany. He was a student of Johann Friedrich Gottlieb Goldhagen who had founded an outpatient clinic called the Schola clinica. In 1787 he became extraordinary professor of medicine at the University of Halle and after Goldhagen’s death he became head of the Schola clinica. There he developed a medical program based heavily on Friedrich Schelling's Naturphilosophie. In 1795, Reil established the first journal of physiology written in German, the Archiv für die Physiologie.
Reil also wrote on Blumenbach's idea of the Bildungstrieb (literally, "building power"), a vital force within each organism that compels it to create, maintain, and repair its form. In Reil's essay "Von der Lebenskraft," he argued that each organism contained a "dormant germ" that was activated by the addition of the father's "animal force."
Reil died on 22 November 1813 from typhus contracted while treating the wounded in the Battle of Leipzig, later known as the Battle of the Nations, one of the most severe confrontations of the Napoleonic Wars.