The California Institute of Technology (branded as Caltech) is a private research university in Pasadena, California. The university is known for its strength in science and engineering, and is among a small group of institutes of technology in the United States which is primarily devoted to the instruction of pure and applied sciences. Caltech is ranked among the best academic institutions in the world and is among the most selective in the U.S.

The institution was founded as a preparatory and vocational school by Amos G. Throop in 1891 and began attracting influential scientists such as George Ellery Hale, Arthur Amos Noyes, and Robert Andrews Millikan in the early 20th century. The vocational and preparatory schools were disbanded and spun off in 1910 and the college assumed its present name in 1920. In 1934, Caltech was elected to the Association of American Universities, and the antecedents of NASA's Jet Propulsion Laboratory, which Caltech continues to manage and operate, were established between 1936 and 1943 under Theodore von Kármán.

Caltech has six academic divisions with strong emphasis on science and engineering, managing $332 million in 2011 in sponsored research. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. First-year students are required to live on campus, and 95% of undergraduates remain in the on-campus House System at Caltech. Although Caltech has a strong tradition of practical jokes and pranks, student life is governed by an honor code which allows faculty to assign take-home examinations. The Caltech Beavers compete in 13 intercollegiate sports in the NCAA Division III's Southern California Intercollegiate Athletic Conference (SCIAC).

Scientists and engineers at or from the university have played an essential role in many modern scientific breakthroughs and innovations, including advancements in sustainability science, quantum physics, earthquake monitoring, protein engineering, and soft robotics. As of October 2021, there are 79 Nobel laureates who have been affiliated with Caltech, including 46 alumni and faculty members (47 prizes, with chemist Linus Pauling being the only individual in history to win two unshared prizes); in addition, 4 Fields Medalists and 6 Turing Award winners have been affiliated with Caltech. There are 8 Crafoord Laureates and 56 non-emeritus faculty members (as well as many emeritus faculty members) who have been elected to one of the United States National Academies, 4 Chief Scientists of the U.S. Air Force and 71 have won the United States National Medal of Science or Technology. Numerous faculty members are associated with the Howard Hughes Medical Institute as well as NASA. According to a 2015 Pomona College study, Caltech ranked number one in the U.S. for the percentage of its graduates who go on to earn a PhD.