Modern dance is a broad genre of western concert or theatrical dance which includes dance styles such as ballet, folk, ethnic, religious, and social dancing; and primarily arose out of Europe and the United States in the late 19th and early 20th centuries. It was considered to have been developed as a rejection of, or rebellion against, classical ballet, and also a way to express social concerns like socioeconomic and cultural factors.

In the late 19th century, modern dance artists such as Isadora Duncan, Maud Allan, and Loie Fuller were pioneering new forms and practices in what is now called improvisational or free dance. These dancers disregarded ballet's strict movement vocabulary (the particular, limited set of movements that were considered proper to ballet) and stopped wearing corsets and pointe shoes in the search for greater freedom of movement.

Throughout the 20th century, sociopolitical concerns, major historical events, and the development of other art forms contributed to the continued development of modern dance in the United States and Europe. Moving into the 1960s, new ideas about dance began to emerge as a response to earlier dance forms and to social changes. Eventually, postmodern dance artists would reject the formalism of modern dance, and include elements such as performance art, contact improvisation, release technique, and improvisation.

American modern dance can be divided (roughly) into three periods or eras. In the Early Modern period (c. 1880–1923), characterized by the work of Isadora Duncan, Loie Fuller, Ruth St. Denis, Ted Shawn, and Eleanor King, artistic practice changed radically, but clearly distinct modern dance techniques had not yet emerged. In the Central Modern period (c. 1923–1946), choreographers Martha Graham, Doris Humphrey, Katherine Dunham, Charles Weidman, and Lester Horton sought to develop distinctively American movement styles and vocabularies, and developed clearly defined and recognizable dance training systems. In the Late Modern period (c. 1946–1957), José Limón, Pearl Primus, Merce Cunningham, Talley Beatty, Erick Hawkins, Anna Sokolow, Anna Halprin, and Paul Taylor introduced clear abstractionism and avant-garde movements, and paved the way for postmodern dance.

Modern dance has evolved with each subsequent generation of participating artists. Artistic content has morphed and shifted from one choreographer to another, as have styles and techniques. Artists such as Graham and Horton developed techniques in the Central Modern period that are still taught worldwide and numerous other types of modern dance exist today.

Modern dance is often considered to have emerged as a rejection of, or rebellion against, classical ballet, although historians have suggested that socioeconomic changes in both the United States and Europe helped to initiate shifts in the dance world. In America, increasing industrialization, the rise of a middle class (which had more disposable income and free time), and the decline of Victorian social strictures led to, among other changes, a new interest in health and physical fitness. "It was in this atmosphere that a 'new dance' was emerging as much from a rejection of social structures as from a dissatisfaction with ballet." During that same period, "the champions of physical education helped to prepare the way for modern dance, and gymnastic exercises served as technical starting points for young women who longed to dance." Women's colleges began offering "aesthetic dance" courses by the end of the 1880s. Emil Rath, who wrote at length about this emerging art form at the time stated,

"Music and rhythmic bodily movement are twin sisters of art, as they have come into existence simultaneously...today we see in the artistic work of Isadora Duncan, Maud Allan, and others the use of a form of dancing which strives to portray in movements what the music master expresses in his compositions—interpretative dancing."

In Europe, Mary Wigman in Germany, Francois Delsarte, Émile Jaques-Dalcroze (Eurhythmics), and Rudolf Laban developed theories of human movement and expression, and methods of instruction that led to the development of European modern and Expressionist dance. Other pioneers included Kurt Jooss (Ausdruckstanz) and Harald Kreutzberg.