State of Decay is the fourth serial of the 18th season in the British science fiction television series Doctor Who, which was first broadcast in four weekly parts from 22 November to 13 December 1980. The serial was the second of three loosely connected serials known as the E-Space trilogy. Adric becomes a companion to the Fourth Doctor in this story having stowed away in the TARDIS at the end of the previous serial, Full Circle.