Mir EO-4 (also called Principal Expedition 4) was the fourth long-duration expedition to the Soviet space station Mir. The expedition began in November 1988, when crew members Commander Aleksandr Volkov and Flight Engineer Sergei Krikalev arrived at the station via the spacecraft Soyuz TM-7. The third crew member of EO-4, Valeri Polyakov, was already aboard Mir, having arrived in August 1988 part way through the previous expedition, Mir EO-3.