Geoffrey Alan Landis (/ˈlændɪs/; born May 28, 1955) is an American aerospace engineer and author, working for the National Aeronautics and Space Administration (NASA) on planetary exploration, interstellar propulsion, solar power and photovoltaics. He holds nine patents, primarily in the field of improvements to solar cells and photovoltaic devices and has given presentations and commentary on the possibilities for interstellar travel and construction of bases on the Moon, Mars, and Venus.

Supported by his scientific background Landis also writes hard science fiction. For these writings he has won a Nebula Award, two Hugo Awards, and a Locus Award, as well as three Rhysling Awards for his poetry. He contributes science articles to various academic publications.

Landis was born in Detroit, Michigan, and lived in Virginia, Maryland, Philadelphia, and Illinois during his childhood. His senior education was at New Trier High School, Winnetka, Illinois. He holds undergraduate degrees in physics and electrical engineering from the Massachusetts Institute of Technology (MIT). He also holds masters degrees in physics and engineering and a PhD in solid-state physics from Brown University. He is married to science fiction writer Mary A. Turzillo and lives in Berea, Ohio.

After receiving his doctorate at Brown University, Landis worked at the NASA Lewis Research Center (now NASA Glenn) and the Ohio Aerospace Institute before accepting a permanent position at the NASA John Glenn Research Center, where he does research on Mars missions, solar energy, and technology development for future space missions. He holds nine patents, and has authored or co-authored more than 300 published scientific papers in the fields of astronautics and photovoltaics.

Landis has commented on the practicalities of generating oxygen and creating building materials for a future Moon base in New Scientist, and on the possibilities of using readily available metallic iron to manufacture steel on Mars.

He is the recipient of numerous professional honors, including the American Institute of Aeronautics and Astronautics Aerospace Power Systems Award, the NASA Space Flight Awareness award and the Rotary National Award for Space Achievement Stellar Award in 2016.

Much of Landis' technical work has been in the field of developing solar cells and arrays, both for terrestrial use and for spacecraft.

Landis has worked on a number of projects related to developing technology of human and robotic exploration of Mars and scientific analysis of the Martian surface, including studies of the performance of photovoltaic cells in the Mars environment, the effect of Martian dust on performance, and technologies for dust removal from the arrays. He was a member of the Rover team on the Mars Pathfinder mission, and named the Mars rock, "Yogi". He is a member of the science team on the 2003 Mars Exploration Rovers mission, where his work includes observations of Martian dust devils, atmospheric science measurements, and observation of frost on the equator of Mars. He was also a member of the Mars ISPP Propellant Precursor experiment team for the Mars Surveyor 2001 Lander mission, an experiment package to demonstrate manufacture of oxygen from the Martian atmosphere (which was cancelled after the failure of the Mars Polar Lander).