Gerardus "Gerard" 't Hooft (Dutch: [ˈɣeːrɑrt ət ˈɦoːft]; born 5 July 1946) is a Dutch theoretical physicist and professor emeritus at Utrecht University, the Netherlands. He shared the 1999 Nobel Prize in Physics with his thesis advisor Martinus J. G. Veltman "for elucidating the quantum structure of electroweak interactions."
His work concentrates on gauge theory, black holes, quantum gravity and fundamental aspects of quantum mechanics. His contributions to physics include: a proof that gauge theories are renormalizable; dimensional regularization; and the holographic principle.
't Hooft was born in Den Helder on 5 July 1946, to Hendrik 't Hooft and Margaretha Agnes 'Peggy' van Kampen, but grew up in The Hague. He was the middle child in a family of three. He comes from a family of scholars. His great-uncle was Nobel Prize laureate Frits Zernike; his maternal grandfather was Pieter Nicolaas van Kampen, a professor of zoology at Leiden University; his uncle Nico van Kampen was a professor emeritus of theoretical physics at Utrecht University, and his father was a maritime engineer. Following his family's footsteps, he showed an interest in science at an early age. When his primary school teacher asked him what he wanted to be when he grew up, he replied, "a man who knows everything."
After primary school Gerard attended the Dalton Lyceum, a school that implemented the Dalton Plan, an educational method that suited him well. He excelled in science and mathematics. At the age of sixteen, he won a silver medal in the second Dutch Math Olympiad.
After 't Hooft passed his secondary-school exams in 1964, he enrolled in the physics program at Utrecht University. He opted for Utrecht instead of the much closer Leiden, because his uncle was a professor there and he wanted to attend his lectures. Since Gerard focused solely on science, his father insisted he join the Utrechtsch Studenten Corps, a student association, in the hope that he would engage in activities outside of studying. To some extent this worked: During his studies he was a coxswain with the rowing club "Triton" and organized a national congress for science students with the science discussion club "Christiaan Huygens".
In the course of his studies, he decided to delve into what he perceived as the heart of theoretical physics: elementary particles. His uncle had grown to dislike the subject and in particular its practitioners. When it became time to write his doctoraalscriptie (former name of the Dutch equivalent of a master's thesis) in 1968, 't Hooft turned to Martinus Veltman, the newly appointed professor who specialized in Yang–Mills theory. At the time, this subject was considered relatively fringe, because it was thought that it could not be renormalized. His assignment was to study the Adler–Bell–Jackiw anomaly, a mismatch in the theory of the decay of neutral pions; formal arguments forbid the decay into photons, whereas practical calculations and experiments showed that this was the primary form of decay. The resolution of the problem was completely unknown at the time, and 't Hooft was unable to provide one.
In 1969, 't Hooft began his doctoral research under the guidance of Martinus Veltman. He worked on the same subject as Veltman: the renormalization of Yang–Mills theories. In 1971 his first paper was published. In it he demonstrated how to renormalize massless Yang–Mills fields, and was able to derive relations between amplitudes. These relations would later be generalized by Andrei Slavnov and John C. Taylor and become known as the Slavnov–Taylor identities.
The world took little notice, but Veltman was excited because he realized that the problem he had been working on had been solved. A period of intense collaboration followed, during which they developed the technique of dimensional regularization. Soon, 't Hooft's second paper was ready to be published, in which he showed that Yang–Mills theories with massive fields due to spontaneous symmetry breaking could be renormalized. This paper earned them worldwide recognition and ultimately won them the 1999 Nobel Prize in Physics.
These two papers formed the basis of 't Hooft's 1972 Ph.D. dissertation The Renormalization Procedure for Yang–Mills Fields. That same year he married Albertha A. Schik, a medical student in Utrecht.
After obtaining his doctorate 't Hooft went to CERN in Geneva, where he held a fellowship. There, he further refined his methods for Yang–Mills theories with Veltman (who had returned to Geneva). During this time, he became interested in the possibility that the strong interaction could be described as a massless Yang–Mills theory. This type of theory he had just proven to be renormalizable, making it susceptible to detailed calculation and comparison with experiments.
According to 't Hooft's calculations, this type of theory possesses just the right kind of scaling properties (asymptotic freedom) that deep inelastic scattering experiments suggest it should have. This was contrary to the popular perception of Yang–Mills theories at the time. Like gravitation and electrodynamics, it was thought that their intensity would decrease with increasing distance between the interacting particles. However, such conventional behavior could not explain the results of deep inelastic scattering, whereas 't Hooft's calculations could.
When 't Hooft mentioned his results at a small conference at Marseille in June 1972, Kurt Symanzik encouraged him to publish them. However, 't Hooft did not, and the findings were later rediscovered and published by Hugh David Politzer, David Gross, and Frank Wilczek in 1973. This led to their receiving the 2004 Nobel Prize in Physics.
In 1974, 't Hooft returned to Utrecht where he became an assistant professor. In 1976, he was invited to take on a guest position at Stanford and a position at Harvard as Morris Loeb Lecturer. His eldest daughter, Saskia Anne, was born in Boston, while his second daughter, Ellen Marga, was born in 1978 after he returned to Utrecht, where he was made full professor. In the 1987–1988 academic year 't Hooft spent a sabbatical in the Boston University Physics Department along with Howard Georgi, Robert Jaffe and others arranged by the then new department chair Lawrence Sulak.
In 2007 't Hooft became the editor-in-chief of Foundations of Physics, where he sought to distance the journal from the controversy of ECE theory and held the position until 2016.
On 1 July 2011 Utrecht University appointed him distinguished professor.
't Hooft lives in Bilthoven. He was married to Albertha A. Schik (Betteke), MD, former anaesthesiologist and occupational health physician, who passed away in July 2026. He has two daughters, Saskia and Ellen, and five grandchildren. He enjoys music and art. His daughter Saskia translated two of his Dutch-language books into English.
In 1999 't Hooft shared the Nobel prize in Physics with his thesis adviser Veltman for "elucidating the quantum structure of the electroweak interactions in physics". Before that time his work had already been recognized by other notable awards. In 1981, he was awarded the Wolf Prize, possibly the most prestigious prize in physics after the Nobel prize. Five years later he received the Lorentz Medal, awarded every four years in recognition of the most important contributions in theoretical physics. In 1995, he was one of the first recipients of the Spinozapremie, the highest award available to scientists in the Netherlands. In the same year he was also honoured with a Franklin Medal. In 1999 he was awarded the High Energy Particle Physics Prize by the European Physical Society. In 2000, 't Hooft received the Golden Plate Award of the American Academy of Achievement. He was awarded a Special Breakthrough Prize in April 2025 in recognition of his contributions to Fundamental Physics across his career.
Since his Nobel Prize, 't Hooft has received a slew of awards, honorary doctorates and honorary professorships. He was knighted commander in the Order of the Netherlands Lion, and officer in the French Legion of Honor. The asteroid 9491 Thooft has been named in his honor, and he has written a constitution for its future inhabitants.