Spectral music as a distinct movement began in 1976, when, within a few days of each other, Murail’s Mémoire-érosion and Grisey’s Partiels were both premiered by Ensemble l’Itinéraire. This chapter explores how, driven by the theorist Dufourt, the young composers associated with l’Itinéraire developed a theoretical identity in contradistinction to Boulez and IRCAM. As well as detailing the salient qualities of Grisey and Murail’s music in this period, the chapter explores the diverse spectral music of Dufourt, Levinas, and Tessier. Dufourt’s works Erewhon, La tempesta d’après Giorgione, and Saturne engage with insights regarding sound related to his encounters with Risset and Chowning. Levinas’s works like Appels foregrounded sonic parasitism and a dramatic spectacle far removed from the more reserved forms of Murail, of which the chapter shows Levinas to have been at times a public critic. Tessier’s music in this period was expressionistic and explored electroacoustic resources. As well as detailing these various spectral sub-currents, the chapter explores the role of l’Itinéraire’s performers in helping to develop performing techniques adequate to the spectral writing.