Global positioning system (GPS) is a technology that allows a receiver to pick up information about its own position and velocity (speed and direction) from satellites in medium Earth orbit. It can provide three dimensional data up to an accuracy of 10 metres. It is officially called NAVSTAR GPS (NAVigation Satellite And Ranging Global Positioning System). GPS was developed by the US Department of Defense. The first satellite was launched in 1978 and now over two dozen satellites are available.

The system is vital for navigation, map-making, and land surveying. It can also be used to provide time references for the study of earthquakes or to synchronize telecommunications networks. It can be used in military applications for precise delivery of intercontinental ballistic missiles (ICBMs), cruise missiles, and precision-guided munitions as well as helping in logistics and nuclear detonation detection.

To work out its position the GPS receiver requires information from at least three satellites. The signals travel at known speed and carry satellite location information. This is enough information to compute receiver position using trilateration (a mathematical method of determining a precise location based on the geometry of triangles). In practice extra satellites may be used in the calculation to correct for inaccuracies in the receiver's clock.

In theory GPS is, as the name suggests, available globally. In practice GPS can be interfered with by electromagnetic radiation overpowering the signal. This can occur naturally through solar flares and the geomagnetic storms found at the poles of the Earth's magnetic field. It also opens up the possibility of deliberately jamming the signal. It is believed that GPS-jamming technology was used against American forces in both Afghanistan and Iraq.

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