The Low-Frequency Array (LOFAR) is a large radio telescope, with an antenna network located mainly in the Netherlands, and spreading across 7 other European countries as of 2019.

This step-wise approach provides great flexibility in setting and rapidly changing the directional sensitivity on the sky of an antenna station.

The six stations in Germany, three in Poland, and one each in France, Great Britain, Ireland, Latvia, and Sweden, with various national, regional, and local funding and ownership.

Italy officially joined the International LOFAR Telescope (ILT) in 2018; construction at the INAF observatory site in Medicina, near Bologna, is planned as soon as upgraded (so-called LOFAR2.0) hardware becomes available.

LOFAR was conceived as an innovative effort to force a breakthrough in sensitivity for astronomical observations at radio-frequencies below 250 MHz.

[5] The electric signals from the LOFAR stations are digitised, transported to a central digital processor, and combined in software in order to map the sky.

[4] To make radio surveys of the sky with adequate resolution, the antennas are arranged in clusters that are spread out over an area of more than 1000 km in diameter.

This installation functions as a VHF receiver either in stand-alone mode or part of a bistatic radar system together with EISCAT transmitter in Tromsø.

LOFAR will be the most sensitive radio observatory at its low observing frequencies until the Square Kilometre Array (SKA) comes online in the late 2020s.

The sensitivities and spatial resolutions attainable with LOFAR make possible several fundamental new studies of the Universe as well as facilitating unique practical investigations of the Earth's environment.

One of the most exciting, but technically most challenging, applications of LOFAR will be the search for redshifted 21 cm line emission from the Epoch of Reionization (EoR).

In February 2021, astronomers released, for the first time, a very high-resolution image of 25,000 active supermassive black holes, covering four percent of the Northern celestial hemisphere, based on ultra-low radio wavelengths, as detected by LOFAR.

[24] The combination of low frequencies, omnidirectional antennae, high-speed data transport and computing means that LOFAR will open a new era in the monitoring of the radio sky.

Transient radio phenomena, only hinted at by previous narrow-field surveys, will be discovered, rapidly localised with unprecedented accuracy, and automatically compared to data from other facilities (e.g. gamma-ray, optical, and X-ray observatories).

LOFAR offers a unique possibility in particle physics for studying the origin of high-energy and ultra-high-energy cosmic rays (HECRs and UHECRs) at energies between 1015–1020.5 eV.

Possible candidate sources of these HECRs are shocks in radio lobes of powerful radio galaxies, intergalactic shocks created during the epoch of galaxy formation, so-called Hyper-novae, gamma-ray bursts, or decay products of super-massive particles from topological defects, left over from phase transitions in the early Universe.

LOFAR opens the window to the so far unexplored low-energy synchrotron radio waves, emitted by cosmic-ray electrons in weak magnetic fields.

LOFAR will also measure the Faraday effect, which is the rotation of polarization plane of low-frequency radio waves, and gives another tool to detect weak magnetic fields.

At the same time, scientific interest in a low-frequency radio telescope began to emerge at ASTRON and at the Dutch Universities.

In accordance with Bsik guidelines, LOFAR was funded as a multidisciplinary sensor array to facilitate research in geophysics, computer sciences and agriculture as well as astronomy.

On April 26, 2005, an IBM Blue Gene/L supercomputer was installed at the University of Groningen's math centre, for LOFAR's data processing.