The Impressionist movement in music is a movement in music loosely set between the late nineteenth century, up to the middle of the twentieth century. Like its precursor in the visual arts, musical impressionism was based in France, and the French composers Claude Debussy and Maurice Ravel are generally considered to be the two "great" impressionists (although Debussy renounced the term, and Ravel composed many other pieces that can't possibly be identified as "Impressionist"). The greatest American impressionist composer is Charles Tomlinson Griffes.
Philosophically, impressionism aimed to convey the atmospheric impact of an event, place, or thing, rather than an accurate portrayal of the subject itself. For instance, Debussy's setting of the Prélude à l'après-midi d'un faune is not a literal portrayal of the events of the already vague poem, but a depiction of the feeling of the poem.
Technically, the impressionists invented or began using a great number of new compositional techniques: multi-modality, planing (the use of voices moving in parallel motion; Debussy's prelude La cathédrale engloutie provides an example), extended tertian harmonies, and intentionally ambiguous musical forms.
Impressionist composers also made extensive use of whole tone scales to create a dreamy, "hazy" effect in their works, much like the vapid paintings of Renoir and Monet. They deliberately abandoned the major-minor scales which had been in use since the seventeenth century. Also, a sharp focus on tone color led to many new possibilities. See List of impressionistic pieces.