In this thesis there has been an attempt made to trace the origin, growth and development, and modification of various tendencies in the Opera. The form only of the opera has been considered and no at-tempt has been made towards the harmonic analysis of the various operas. The main tendencies that have been discussed are, the differ-ences in regard to; (1) the number of acts employed; (2) the number and kind of characters; (3) a comparison; (a) of the proportion of or-chestral work, overtures, ballets and ritornelli; (b) of solo work and the various voices employed; (c) of recitative, spoken, accompanied and unaccompanied; (d) of ensemble work, duets, trios, quartets, quintets and sextets; and (e) separate from this last, a consideration of the proportion of chorus work, mixed, and that sung by the men and the women alone.