The Mars Reconnaissance Orbiter is a $720 million USD spacecraft built by Lockheed Martin under the supervision of Jet Propulsion Laboratory (JPL) for the purpose of orbiting Mars, mapping its surface in great detail, and studying the Martian climate, weather, atmosphere, and geology. The craft was launched 12 August 2005, on board an Atlas V booster, and took approximately seven months to make the trip to Mars, entering low Mars orbit on 10 March 2006. In November 2006, it started making its primary observations. It will continue those observations until November 2008, when it may be granted a mission extension for good behavior.

The Mars Reconnaissance Orbiter is one among five other spacecraft on or orbiting Mars. The others are the Mars Global Surveyor, Mars Express, Mars Odyssey, and two Mars Exploration Rovers. All of these except for the Mars Express, which was sent by the European Space Agency, are the property of NASA. Part of the Mars Reconnaissance Orbiter's mission is to identify promising landing zones for future Mars Rovers, such as the Phoenix lander in 2008 and the Mars Science Laboratory in 2010. NASA has announced that its long-range plan (2025) is a manned mission to Mars.

After arriving at Mars, the orbiter entered into a long, elliptical orbit, and used the technique of aerobraking - intentionally dipping low into the atmosphere - to slow itself down and achieve a more suitable orbit for observations. Its current orbit places it 250 to 316 km (155 to 196 mi) above the surface, a bit lower than the International Space Station orbits the Earth. Low Mars Orbit is slightly lower than Low Earth Orbit because of Mars' lower gravity.

Two of the Mars Reconnaissance Orbiter's most interesting discoveries have been a few signs of the past presence of liquid water and the discovery of large, dark holes, thought to be cave entrances. The orbiter's signature instrument, the HiRISE (High Resolution Imaging Science Experiment) camera, is capable of taking photos of the Martian surface to a resolution of 0.3 m per pixel, in comparison to 0.1 m per pixel for the best Earth-orbiting satellites and 1 m per pixel for Google Maps. HiRISE's data has allowed for the creation of a Google Mars. SHARAD, the Shallow Subsurface Radar, is another instrument designed to look under the surface of Mars using radar waves. It can resolve underground features up to 1 km deep at a resolution of 7 m.