Guido da Arezzo Musica Classica Classical Music Dictionary entry with life and illustrations. http://www.karadar.net/Dictionary/arezzo.html

Guido of Arezzo Catholic Encyclopedia article with life and summary of contributions to musical theory and composition. http://www.newadvent.org/cathen/07065a.htm

Guido of Arezzo Biography emphasizing his work as theorist and teacher, crediting his influence on countless Middle Ages composers and musicians, and noting major developments. From the Grove Concise Dictionary of Music entry at WQXR radio. http://www.wqxr.com/cgi-bin/iowa/cla/learning/grove.html?record=3929

Guido d'Arezzo, (c. 0995 - c. 1050), France/Italy Biographical data, recommended CDs, books and sheet music, bibliography, and links to biographical essays from Dr. Estrella's Incredibly Abridged Dictionary of Composers. http://www.stevenestrella.com/composers/index.html?composerfiles/guido1050.html

Gabrieli, Andrea (c. 1510 - 1586), Italy Biographical data, recommended CDs, books and sheet music, bibliography, and links to biographical essays from Dr. Estrella's Incredibly Abridged Dictionary of Composers. http://stevenestrella.com/composers/index.html?composerfiles/gabrieli1585.html