After the internal conflicts of the 19th century, Buenos Aires was federalised and removed from Buenos Aires Province; its city limits were enlarged to include the former towns of Belgrano and Flores (both are now neighbourhoods in the city). Argentines sometimes refer to the city as Capital Federal to differentiate the city from the province of the same name. In the 1994 constitution, it was declared an Autonomous City (hence the formal denomination Ciudad Autónoma de Buenos Aires).

Buenos Aires was home for Argentine writers Jorge Luis Borges, Adolfo Bioy Casares, Ernesto Sábato and Victoria Ocampo. Writer Julio Cortázar, who was born in Brussels, lived for a long period in Buenos Aires, before relocating to France where he died. International figures who lived in Buenos Aires include artists René Goscinny, Marcel Duchamp, Witold Gombrowicz, Jerry Masucci, and businessmen John S. Reed and Aristotle Onassis. During the Spanish Civil War and in its aftermath, Buenos Aires provided refuge for many, including philosopher José Ortega y Gasset.

The University of Buenos Aires, which still remains one of the top learning institutions in South America, has produced five Nobel Prize winners and provides free education for students from all around the globe. For much of the 20th century, Buenos Aires was the cultural capital of the Spanish-speaking world, and many porteños flaunted their riches abroad (for example, famed New York nightclub El Morocco was owned by a porteño playboy). This gave birth to a stereotype of Argentines as vain and arrogant that became widespread across Latin America; some (especially Uruguayans) make the distinction between porteños and provincianos (people from the provinces), who are excluded from this characterization.

Tango was originally danced only with male partners, because it was deemed too sexually explicit to dance with a man and a woman. In 1902, the Teatro Opera started organising tango balls. In the 1920s, tango was adopted by the Parisian high society and then all over the world. The Buenos Aires style of tango music evolved into an elaborated genre. In its heyday, tango had many famous orchestras such as those led by Aníbal Troilo and Juan D'Arienzo, and singers such as Carlos Gardel and Edmundo Rivero.

Buenos Aires now holds an annual "Tango Day" each December 11. In San Telmo, Sundays are devoted to tango shows on the streets and antiques trade in the bazaars around Dorrego Square.