In Search of... is an American television series that was broadcast weekly from 1976 to 1982, devoted to mysterious phenomena. It was created after the success of three one-hour documentaries produced by creator Alan Landsburg: In Search of Ancient Astronauts in 1973 (based on the 1968 book/ 1970 film Chariots of the Gods? by Erich von Däniken), In Search of Ancient Mysteries (1974), and The Outer Space Connection in 1975 (later adapted into popular paperbacks written by Landsburg), all of which featured narration by Rod Serling, who was the initial choice to host the spin-off show. Serling died before production started, and Leonard Nimoy was then selected to be the host. The series was revived with host Mitch Pileggi in 2002 and again in 2018 with Zachary Quinto for the History channel.

The original series was shown in Australia in the 1980s under the title Great Mysteries of the World, with each episode having an introduction and conclusion presented by television presenter Scott Lambert.