Einstein@Home is a volunteer computing project that searches for signals from spinning neutron stars in data from gravitational-wave detectors, from large radio telescopes, and from a gamma-ray telescope. Neutron stars are detected by their pulsed radio and gamma-ray emission as radio and/or gamma-ray pulsars. They also might be observable as continuous gravitational wave sources if they are rapidly spinning and non-axisymmetrically deformed. The project was officially launched on 19 February 2005 as part of the American Physical Society's contribution to the World Year of Physics 2005 event.

Einstein@Home searches data from the LIGO gravitational-wave detectors. The project conducts the most sensitive all-sky searches for continuous gravitational waves. While no such signal has yet been detected, the upper limits set by Einstein@Home analyses provide astrophysical constraints on the galactic population of spinning neutron stars in our Milky Way galaxy.

Einstein@Home also searches radio telescope data from the Arecibo Observatory, and has in the past analyzed data from Parkes Observatory. On 12 August 2010, the first discovery by Einstein@Home of a previously undetected radio pulsar J2007+2722, found in data from the Arecibo Observatory, was published in Science. This was the first data-based discovery by a volunteer computing project. As of December 2023, Einstein@Home had discovered 55 radio pulsars.

The project also analyses data from the Fermi Gamma-ray Space Telescope to discover gamma-ray pulsars. On 26 November 2013, the first Einstein@Home results of the Fermi data analysis was published: the discovery of four young gamma-ray pulsars in data from Fermi's Large Area Telescope (LAT). As of December 2023, Einstein@Home has discovered 39 previously unknown gamma-ray pulsars in data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. The Einstein@Home search makes use of novel and more efficient data-analysis methods and discovered pulsars missed in other analyses of the same data.

The project runs on the Berkeley Open Infrastructure for Network Computing (BOINC) software platform and uses free software released under the GNU General Public License, version 2. Einstein@Home is hosted by the Max Planck Institute for Gravitational Physics (Albert Einstein Institute, Hannover, Germany) and the University of Wisconsin–Milwaukee. The project is supported by the Max Planck Society (MPG), the American Physical Society (APS), and the US National Science Foundation (NSF). The Einstein@Home project director is Bruce Allen.

Einstein@Home uses the power of volunteer computing in solving the computationally intensive problem of analyzing a large volume of data. Such an approach was pioneered by the SETI@home project, which is designed to look for signs of extraterrestrial life by analyzing radio wave data. Einstein@Home runs through the same software platform as SETI@home, the Berkeley Open Infrastructure for Network Computing (BOINC). As of December 2023, more than 492,000 volunteers in 226 countries had participated in the project, making it the third-most-popular active BOINC application. Users regularly contribute about 7.7 petaFLOPS of computational power, which would rank Einstein@Home among the top 105 on the TOP500 list of supercomputers.

The Einstein@Home project was originally created to perform all-sky searches for previously unknown continuous gravitational-wave (CW) sources using data from the Laser Interferometer Gravitational-Wave Observatory (LIGO) detector instruments in Washington and Louisiana, USA. The best understood potential CW sources are rapidly spinning neutron stars (including pulsars) which are expected to emit gravitational waves due to a deviation from Rotational symmetry. Besides validating Einstein's theory of General Relativity, direct detection of gravitational waves would also constitute an important new astronomical tool. As most neutron stars are electromagnetically invisible, gravitational-wave observations might also reveal completely new populations of neutron stars. A CW detection could potentially be extremely helpful in neutron-star astrophysics and would eventually provide unique insights into the nature of matter at high densities, because it provides a way of examining the bulk motion of the matter.

Since March 2009, part of the Einstein@Home computing power has also been used to analyze data taken by the PALFA Consortium at the Arecibo Observatory in Puerto Rico. This search effort is designed to find radio pulsars in tight binary systems. It is expected that there is one radio pulsar detectable from Earth in an orbital system with a period of less than one hour. A similar search has also been performed on two archival data sets from the Parkes Multi-beam Pulsar Survey. The Einstein@Home radio pulsar search employs mathematical methods developed for the search for gravitational waves.