Though no one now living is likely to have ever heard a castrato voice and the few recordings that exist are, for a number of reasons, ei- ther of dubious authenticity or of aged church castrati recorded under less than optimal circumstances, there is considerable material available about the castrato voice, particularly as exemplified by seventeenth- and eighteenth-century castrati trained to sing opera when the castrato dom- inated the stage in Italian opera serta and operas modeled on that genre. Those castrati have to be differentiated from the castrati who were church singer namely, singers whose voices and/or techniques were not good enough for opera. Castrati were actually divided into two vocal categories: the soprano castrato and the alto castrato, Thus, the castrato perhaps best known to us, Farinelli, was a soprano, while the castrato Handel employed most, Senesino, was an alto. The differentiation is a matter of range, in much the same (but probably not the identical) way that a female soprano differs from a female mezzo-soprano.