A voice type is a group of voices with similar vocal ranges, capable of singing in a similar tessitura, and with similar vocal transition points (passaggi). Voice classification is most strongly associated with European classical music, though it, and the terms it utilizes, are used in other styles of music as well.
A singer will choose a repertoire that suits their voice. Some singers such as Enrico Caruso, Rosa Ponselle, Joan Sutherland, Maria Callas, Jessye Norman, Ewa Podleś, and Plácido Domingo have voices that allow them to sing roles from a wide variety of types; some singers such as Shirley Verrett and Grace Bumbry change type and even voice part over their careers; and some singers such as Leonie Rysanek have voices that lower with age, causing them to cycle through types over their careers. Some roles are hard to classify, having very unusual vocal requirements; Mozart wrote many of his roles for specific singers who often had remarkable voices, and some of Verdi's early works make extreme demands on their singers.