The Chicago Theological Seminary (CTS) is a Christian ecumenical American seminary located in Chicago, Illinois, and is one of several seminaries historically affiliated with the United Church of Christ. It is the oldest institution of higher education in Chicago, originally established in 1855 under the direction of the abolitionist Stephen Peet and the Congregational Church (now the United Church of Christ) by charter of the Illinois legislature.

In addition to being a seminary of the United Church of Christ, CTS offers students coursework necessary to be ordained by the Metropolitan Community Church denomination. It was the first theological school to introduce the field education experience into a seminary curriculum, the first to create a distinct Department of Christian Sociology in an American theological school, and the first seminary to award a degree in divinity to a woman in the United States (Florence Fensham, 1902).

Unintimidated by controversy, Chicago Theological Seminary has a record of setting trends in American faith life and leadership for more than a century.

In the 1850s and 1860s, CTS founder Stephen Peet was a leader in a new generation of 19th-century American abolitionists no longer content to wait for the end of slavery nor to tolerate those who defended it. Under his leadership, the seminary was active in the Underground Railroad and was a leading voice in the Christian Abolitionism movement.

The first CTS curriculum in 1855 was provided for students among congregations and missions across the Midwest. Students were encouraged to learn by direct experience the facts of community life and church needs in an experimental culture. Although such a practice was unknown at that time, this curriculum was the beginning of the first field education component introduced into seminary education. Field education is now a part of every accredited professional theological degree program.

Because of a conviction that training for ministry needed to combine the study of Christian faith and the world of secular knowledge and action, during President Ozora Davis' tenure in 1900s, CTS moved to the vicinity of the University of Chicago. Under Ozora Davis' leadership the buildings of the seminary were financed and constructed, and the relationship with the University of Chicago established.

After recognizing Florence Fensham with the first American seminary degree awarded to a woman, Chicago Theological Seminary founded the Congregational Training School for Women in 1909 to provide Congregational women with advanced educational training. The school continued its mission until it was subsumed into the Chicago Theological Seminary in 1926. Florence Fensham was the school's first dean, succeeded by Agnes M. Taylor and Margaret M. Taylor after Dean Fensham died unexpectedly in 1912. The Chicago Theological Seminary allow full acceptance of women to its programs in 1926, thereby eliminating the need for a separate institution for women.

In 1892, CTS invited Graham Taylor, a professor of theology at Hartford Theological Seminary in Connecticut who had shown success in working with the poor, to establish the United States' first Department of Christian Sociology at CTS. Taylor worked closely with leading Chicago activist Jane Addams, founder of Hull House, an American settlement house. Taylor established the Chicago Commons settlement house in Chicago's Fulton Market neighborhood, where with the help of CTS students he brought recreational clubs, classes, a day nursery, and a kindergarten to the working poor. The house had 25 residents and was open to all ethnic groups and religious denominations. Pressed for space, the Chicago Commons moved a few blocks north to the building formerly occupied by the Chicago Congregational Tabernacle, where Taylor expanded the courses offered into the Chicago School of Civics and Philanthropy, which later became the University of Chicago School of Social Service Administration.