LOFAR is the LOw Frequency ARray for radio astronomy. It is an ambitious project to build an interferometric array of radio telescopes distributed across the Netherlands and Northern Germany, with a total effective collecting area of up to 1 square kilometre. The processing of the data is done by a supercomputer situated at the University of Groningen.

LOFAR started as a new and innovative effort to force a breakthrough in sensitivity for astronomical observations at radio-frequencies below 250 MHz. Astronomical radio interferometers usually consist either of arrays of parabolic dishes (e.g. the One-Mile Telescope), arrays of one-dimensional antennas (e.g. the Molonglo Observatory Synthesis Telescope) or two-dimensional arrays of omni-directional dipoles (e.g. Tony Hewish's Pulsar Array). LOFAR combines aspects of many of these earlier telescopes — in particular it uses the omni-directional dipole antennae as a phased array using the aperture synthesis technique developed in the 1950s. Like the earlier CLFST low-frequency radio telescope, the design of LOFAR has concentrated on the use of large numbers of relatively cheap antennas, with the mapping performed using aperture synthesis software.

The electronic signals from the LOFAR antennas are digitised, transported to a central digital processor, and combined in software in order to map the sky. The cost is dominated by the cost of electronics and will follow Moore's law, becoming cheaper with time and allowing increasingly large telescopes to be built. So LOFAR is an IT-telescope. The antennas are simple enough but there are a lot of them — 25000 in the full LOFAR design. To make radio pictures of the sky with adequate sharpness, these antennas are to be arranged in clusters that are spread out over an area of ultimately 350 km in diameter. The currently funded first phase contains 15000 antennas, reaching baselines of 100 km. Data transport requirements are in the range of many Tera-bit/s and the processing power needed is tens of Tera-FLOPS.

The mission of LOFAR is to survey the universe at radio frequencies from ~10–240 MHz with greater resolution and greater sensitivity than previous surveys, such as the 7C and 8C surveys, and surveys by the Very Large Array (VLA) and Giant Meterwave Radio Telescope (GMRT).

LOFAR will be the most sensitive radio observatory until the next generation of large array radio telescope, the Square Kilometre Array (SKA), comes online around 2020.