A prodigy who started playing the piano at age 3, Agay was born and raised near Budapest, Hungary and moved to New York in 1939 as Nazism rose in his native country, the Baltimore Sun said.
In the late 1940s, Agay began a career in teaching, composing and publishing. He was conductor and arranger for the NBC radio show "Guest Star," which featured such movie and musical stars as Bing Crosby, the Andrews Sisters and Perry Como.
The author of 96 books, Agay is best known for his teaching collections, anthologies and texts for piano studies, notably the "Joy of ..." series and "Easy Classics to Moderns" series.
He wrote "An Anthology of Piano Music," that covered the Baroque, classical, Romantic and 20th Century periods. Another work is "Best Loved Songs of the American People," originally published in 1975, included ballads, spirituals, burlesque and vaudeville tunes, jazz and blues.
Agay, who died Jan. 24, is survived by his daughter and three grandsons.