Historical Tenors
- Discographies, repertoires, and short biographies of many tenors.
- http://www.francoisnouvion.net/

Tenorland
- Biographies, links, and sound clips of the great tenors.
- http://www.tenorland.com/

(Un)official Countertenor Homepage, The
- Directory of mini biographies of countertenors. Other music links.
- http://www.medieval.org/emfaq/performers/countertenors.html

Urban Dictionary: Contralto
- Offers several informal definitions contributed by submitters.
- http://www.urbandictionary.com/define.php?term=contralto

Special Considerations in the Training of the Bass Singer
- Page from VoiceTeacher.com defines differences between basso profundo, basso cantablie (or lyrical bass), and bass-baritone.
- http://www.voiceteacher.com/bass_voice.html

Voice Definitions and Ranges
- Explains how the names of polyphonic parts were adapted to identify voice types, with emphasis on the tenor and countertenor.
- http://www.medieval.org/emfaq/misc/voices.html

History of the Tenor Voice
- Paper from the first international conference on Physiology and Acoustics of Singing (PAS), held in the Netherlands in 2002.
- http://www.med.rug.nl/pas/Conf_contrib/Reinders/Reinders_the_way_tenor.htm

Wikipedia: Baritone
- Defines the singing range as lower than tenor but higher than bass, with subclassifications including lyric, bel canto and dramatic.
- http://en.wikipedia.org/wiki/Baritone

Wikipedia: Soprano
- Lengthy article describes vocal quality and typical range for subtypes from coloratura to dramatic, with a list of soprano roles in the operatic and musical theater repertoire.
- http://en.wikipedia.org/wiki/Soprano