The common practice period is the approximately two-and-a-half century span from roughly 1650 to 1900 or from the mid- to late Baroque period, through the Classical, Romantic and Impressionist periods, encompassing the formation and eventual decline of the tonal system and the standardization of the techniques, written form and ideas of Western European music. Most of the classical music commonly heard today was composed during this span.
Although the common practice period saw a rapid evolution of and vast differences in style, it was unified by the use of a harmonic system that was almost always derived from a single tonal center and to which modern music theorists can apply a consistent analysis using Roman numerals.