Perotin (Latin Perotinus) was a most gifted composer of the Notre Dame school, which, during the late twelfth and early thirteenth centuries, was the first school to produce polyphony of international acclaim. Four of the works included in this collection are organa. A Perotin organum consists of a liturgical chant melody and text, which forms the tenor or cantus firmus. Its rhythm is altered. In approximately the same vocal range, the composer added one, two or three other voices, the duplum, triplum and quadruplum, all of them in one of the six rhythmic patterns known as modi. Seven of the works included in this collection are motets. These originated throug the tradition of troping, which consisted of the addition of a text to a melismatic piece of music. In motets, it was the duplum of an organum or clausula which was troped. When this happend the duplum was called motetus, and this name was adapted for the entire composition.