"In Purgatory's Shadow" is the 112th episode of the television series Star Trek: Deep Space Nine, the 14th episode of the fifth season. The episode premiered on February 10, 1997 to a Nielsen rating of 6.7 points. It is the first half of a two-part episode, with the second half, "By Inferno's Light", first airing a week later.

Set in the 24th century, the series follows the adventures of the crew of the space station Deep Space Nine near the planet Bajor, as the Bajorans recover from a decades-long occupation by the imperialistic Cardassians. The station is adjacent to a wormhole connecting the Alpha and Gamma Quadrants of the galaxy; the Gamma Quadrant is home to an expansionist empire known as the Dominion, ruled by the shape-shifting Changelings. This episode begins the Dominion's invasion of the Alpha Quadrant, a plot arc which continues until the final episode of the series. It features the return of several characters, drawing on plot lines previously established in the third, fourth and fifth seasons.

This episode is dedicated "In memory of Derek Garth", a grip for the series who died in an automobile accident in December, eight weeks before the episode aired.