Abraham (Avi) Loeb is the Frank B. Baird, Jr. Professor of Science at Harvard University. He serves as Chair of the Harvard Astronomy department and Director of the Institute for Theory and Computation (ITC).

Loeb received a PhD in plasma physics at age 24 from the Hebrew University of Jerusalem (1986) and was subsequently a long-term member at the Institute for Advanced Study in Princeton (1988-2003), where he started to work in theoretical astrophysics. In 1993 he moved to Harvard University as an Assistant Professor in the Department of Astronomy, where he was tenured three years later. He also holds a visiting professorship at the Weizmann Institute of Science and a Sackler Senior Professorship by special appointment in the School of Physics and Astronomy at Tel Aviv University. Loeb has authored nearly 500 research articles and 3 books.

Loeb has worked on a broad range of research areas in astrophysics and cosmology, including the first stars, the epoch of reionization, the formation and evolution of massive black holes, gravitational lensing by planets, gamma-ray bursts (GRBs) at high redshifts, 21-cm cosmology, the use of the Lyman-alpha forest to measure the acceleration/deceleration of the universe in real time, the future collision between the Milky Way and Andromeda galaxies, the future state of extragalactic astronomy, astrophysical implications of black hole recoil in galaxy mergers, and the imaging of black hole silhouettes. Some of his papers (e.g., the first paper dedicated to planet microlensing (Gould & Loeb 1992), the first paper to suggest that the cosmic acceleration can be measured in real time with the Lyman-alpha forest (Loeb 1998), as well as early papers on high-redshift GRBs, and 21-cm cosmology) are considered pioneering work in areas that have become the focus of established communities of astrophysicists. Loeb was among the very first theorists to initiate the research frontier on the "cosmic dawn" of the first stars and galaxies. He wrote some of the seminal theory papers that laid the foundation for 3D intensity mapping of reionization using the 21-cm line of hydrogen and other spectral lines. Several observatories around the globe (such as LOFAR, MWA, PAPER, and GMRT) were constructed recently in an attempt to detect the predicted 21-cm signal. In additional papers with his students (such as Daniel Eisenstein, Zoltan Haiman, Rosalba Perna, Steve Furlanetto, Joey Munoz, and Eli Visbal) and postdocs (such as Stuart Wyithe, Jonathan Pritchard, and Bence Kocsis), Loeb addressed how and when the first stars and black holes formed and which effects they had on the young universe.

Examples for novel insights offered in Loeb's papers on the epoch of reionization include: the first suggestion that gamma-ray burst afterglows are detectable at high redshifts (with Ciardi), the first study of polarized Lyman-alpha halos in the neutral intergalactic medium around high-redshift galaxies (with Rybicki), the first calculation of 21-cm brightness fluctuations before reionization (with Zaldarriaga), the first suggestion to use the line-of-sight anisotropy in the power spectrum of 21-cm brightness fluctuations due to peculiar velocities for separating the gravitational physics from the astrophysics during reionization (with Barkana), the first demonstration that baryonic acoustic oscillations in 21-cm observations after reionization are detectable (with Wyithe), and the first demonstration that 3D intensity mapping of multiple metal emission lines from high-redshift galaxies can be used to trace large scale structures without resolving individual galaxies (with Visbal). In 2003, Loeb and Gaudi proposed a new technique for detecting exoplanets through relativistic beaming of their parent star; this technique was used to discover the Jupiter size exoplanet Kepler 76b a decade later.

Several of Loeb's predictions received confirmation in 2013. The relativistic beaming technique for detecting planets, proposed by Loeb and Gaudi in 2003, was used to discover the "Einstein planet" Kepler 76b. Following the novel proposal by Pfahl and Loeb in 2004 to search for pulsars as probes of the spacetime around the supermassive black hole SgrA* , a pulsar was discovered in the vicinity of SgrA*. Pani and Loeb ruled out in 2013 the possibility that the dark matter is made of primordial black holes in the range between the masses of the moon and the Sun, and this result was confirmed shortly afterwards by Kepler microlensing limits. Finally, a hypervelocity star candidate from the Andromeda galaxy had been discovered, as predicted by Sherwin, Loeb, and O'Leary in 2008.

Loeb was featured in a cover story of TIME Magazine on the first stars (2006) and in a cover story of Smithsonian Magazine on black holes (2008). He also wrote two Scientific American articles on the dark ages of the Universe (2006) and on the imaging of black hole silhouettes (2009). His book, "How Did the First Stars and Galaxies Form?", was published by Princeton University Press in 2010 and won the 2013 Chambliss Award for Scientific Writing by the American Astronomical Society. His advanced (540 pages long) textbook with Steve Furlanetto, "The First Galaxies in the Universe", was published in December 2012.

Loeb was awarded the Kennedy prize (1987) and the Guggenheim Fellowship (2002). He was the Salpeter Lecturer at Cornell University (2006), the Bahcall Lecturer at Tel Aviv University (2006), the Merle Kingsley Distinguished Visitor at Caltech (2007), the Australian Institute of Physics Lecturer at University of Melbourne (2007), the Distinguished Visiting Lecturer at the Carnegie Observatories (2009), and most recently was awarded the Las Cumbres Observatory Prize Lectureship at UC Santa Barbara (2011), the Sackler Lectureship at Leiden Observatory in the Netherlands (2011), the Galileo Galilei Chair (Cattedra Galileiana) at Scuola Normale Superiore in Pisa, Italy (2012), and the Miegunyah Distinguished Visiting Fellowship at the University of Melbourne, Australia (2013). In 2012 Loeb was elected as a member in the American Academy of Arts and Sciences.