Mixed-sex education (also known as coeducation), is the integrated education of males and females in the same institution. The opposite situation is described as single-sex education. Most older institutions of higher education restricted their enrollment to a single sex at some point in their history, and since then have changed their policies to become coeducational.
The first mixed-sex institution of higher learning in China was the Nanjing Higher Normal School, which was renamed National Central University and Nanjing University. For thousands of years in China, public schools especially public higher learning schools were for men, generally only schools established by zongzu (宗族, gens) for both male and female students. Somes schools such as Li Zhi's school in Ming Dynasty and Yuan Mei's school in Qing Dynasty enrolled both male and female students. In the 1910s women's universities were established such as Ginling Women's University and Peking Girls' Higher Normal School, but there were no coeducation in higher learning schools.
Tao Xingzhi, the Chinese advocator of mixed-sex education, proposed The Audit Law for Women Students (規定女子旁聽法案) at the meeting of Nanjing Higher Normal School held on December 7, 1919. He also proposed that the university recruit female students. The idea was supported by the president Guo Bingwen, academic director Liu Boming, and such famous professors as Lu Zhiwei and Yang Xingfo, but opposed by many famous men of the time. The meeting passed the law and decided to recruit women students next year. Nanjing Higher Normal School enrolled eight Chinese women students in 1920. In the same year Peking University also began to allow women students to audit classes. One of the most notable female students of that time was Jianxiong Wu.
In 1949, the People's Republic of China was founded. The government of PRC has provided equal opportunities for education since then, and all schools and universities have become mixed-sex. In recent years, however, many female and/or single-sex schools have again emerged for special vocational training needs but equal rights for education still apply to all citizens.
Girls admission to Sorbonne was open in 1860. . The baccalaureat became gender-blind in 1924, giving equal chances to all girls in applying to any universities. The mixed-sex education became mandatory for primary schools in 1957 and for all universities in 1975. 
St. Paul's Co-educational College was the first mixed-sex secondary school in Hong Kong. It was founded in 1915 as St. Paul's Girls' College. At the end of World War II it was temporarily merged with St. Paul's College, which is a boys' school. When classes at the campus of St. Paul's College were resumed, it continued to be mixed, and changed to its present name.
In the United Kingdom the official term is mixed, and today most schools are mixed. A number of Quaker co-educational boarding schools were established before the 19th century. In England the first non-Quaker public mixed-sex boarding school was Bedales School, founded in 1893 by John Haden Badley and becoming mixed in 1898. The Scottish Dollar Academy claims to be the first mixed-sex boarding school in the UK (in 1818). Many previously single-sex schools have begun to accept both sexes in the past few decades; for example, Clifton College began to accept women in 1987.
The first United Kingdom university to allow ladies to enter on equal terms with gentlemen, and hence be admitted to academic degrees, was the University of London in 1878, with degrees being conferred upon the United Kingdom's first four female graduates in 1880. The first institution engaged in educating students, given the University of London's then role was an examining authority, to become fully co-educational was University College London in 1878. The University of Cambridge allowed women to take its examinations in 1881 but refused to confer degrees upon women until 1948. The University of Oxford allowed women to take its examinations in 1884 but refused to admit female graduands to the degrees if they passed the said oral examinations until 1920.
The first coeducational institution of higher education in the United States was Franklin College in Lancaster, Pennsylvania, established in 1787. Its first enrollment class in 1787 consisted of 78 male and 36 female students. Among the latter was Rebecca Gratz, the first Jewish female college student in the United States. However, the college began having financial problems and it was reopened as an all-male institution. It became co-ed again in 1969 under its current name, Franklin and Marshall College.
The longest continuously operating coeducational school in the United States is Oberlin College in Oberlin, Ohio, which was established in 1833. The first four women to receive bachelor's degrees in the United States earned them at Oberlin in 1841. Later, in 1862, the first Black woman to receive a bachelor's degree (Mary Jane Patterson) also earned it from Oberlin College.
The University of Iowa became the first public or state university in the United States to admit women, and for much of the next century, public universities, and land grant universities in particular, would lead the way in higher education coeducation. Many other early coeducational universities, especially west of the Mississippi River, were private, such as Carleton College (1866), Texas Christian University (1873), and Stanford University (1891).
At the same time, according to Irene Harwarth, Mindi Maline, and Elizabeth DeBra, "women's colleges were founded during the mid- and late-19th century in response to a need for advanced education for women at a time when they were not admitted to most institutions of higher education" . A notable example are the prestigious Seven Sisters. Of the seven, Vassar College is now coeducational and Radcliffe College has merged with Harvard University. Wellesley College, Smith College, Mount Holyoke College, Bryn Mawr College, and Barnard College are still women's colleges.
Other notable women's colleges that have become coeducational include Ohio Wesleyan Female College in Ohio, Skidmore College, Wells College, and Sarah Lawrence College in New York state, Goucher College in Maryland and Connecticut College.
In U.S.A slang, "Coed" is an informal term for a female student attending a formerly all-male college or university (or any university). This usage reflects the historical process by which it was often female pupils who were admitted to schools originally reserved for boys, and thus it was they who were identified with its becoming "coeducational". The word is also often used to describe a situation in which both sexes are integrated in any form (e.g. "The team is co-ed").