Ragtime (alternately spelled Rag-time) is an American musical genre which enjoyed its peak popularity between 1899 and 1918. It has had several periods of revival since then and is still being composed today. Ragtime was the first truly American musical genre, predating jazz . It began as dance music in popular music settings years before being published as popular sheet music for piano. Being a modification of the then popular march, it was usually written in 2/4 or 4/4 time (meter) with a predominant left hand pattern of bass notes on odd-numbered beats and chords on even-numbered beats accompanying a syncopated melody in the right hand. A composition in this style is called a "rag". A rag written in 3/4 time is a "ragtime waltz".

Ragtime is not a "time" (meter) in the same sense that march time is 2/4 meter and waltz time is 3/4 meter; it is rather a musical genre that uses an effect that can be applied to any meter. The defining characteristic of ragtime music is a specific type of syncopation in which melodic accents occur between metrical beats. This results in a melody that seems to be avoiding some metrical beats of the accompaniment by emphasizing notes that either anticipate or follow the beat. The ultimate (and intended) effect on the listener is actually to accentuate the beat, thereby inducing the listener to move to the music. Scott Joplin, the composer/pianist known as the "King of Ragtime", called the effect "weird and intoxicating". He also used the term "swing" in describing how to play ragtime music: "Play slowly until you catch the swing...". The name swing later came to be applied to an early genre of jazz that developed from ragtime. Converting a non-ragtime piece of music into ragtime by changing the time values of melody notes is known as "ragging" the piece. Original ragtime pieces usually contain several distinct themes, four being the most common number.

According to the New Grove Dictionary of Jazz the musical form was originally called "ragged time" which later became corrupted to "ragtime".