Matthias Josef Maurer (born 18 March 1970) is a German ESA astronaut and materials scientist, who was selected in 2015 to take part in space training.

His dissertation titled "Lightweight composites made of aluminium foam with thermally sprayed coatings" won him several scientific prizes.

Before he formally joined the European Astronaut Corps in July 2015, Maurer took a lead role in ESA Astronaut Centre projects to prepare for future spaceflight and lunar operations with new international partners and extend the Agency's human exploration expertise beyond the International Space Station.

He traveled to the International Space Station alongside NASA astronauts Raja Chari, who commanded the Crew Dragon, Thomas Marshburn, as the pilot, and mission specialist Kayla Barron.

As part of Expedition 66, Maurer and Chari installed ammonia jumpers on the P1 Truss and repositioned a radiator beam valve module which had been giving them trouble returning the unit to operation.

The astronauts routed cables, installed cable clamps on the Bartolomeo platform, tied back thermal insulation on the Kibo Exposed Facility Berthing Mechanism, replaced Camera 8 on the truss which has a bad filter and light, outfitted the radiator grapple bars for a future spacewalk, and also did other maintenance task outside the station.