"Synchrony" is the nineteenth episode of the fourth season of the American science fiction television series The X-Files. It was written by Howard Gordon and David Greenwalt and directed by James Charleston. The episode aired in the United States on April 13, 1997, on the Fox network. The episode is a "Monster-of-the-Week" story, a stand-alone plot, unconnected to the series' wider mythology. "Synchrony" earned a Nielsen rating of 11.3, being watched by 18.09 million people upon its initial broadcast. The episode received mixed to positive reviews from television critics.