While performance studies long have been keen to analyzing orchestral recordings and questioning the creative roles in orchestral music, research on conducting as an activity remains almost non-existent. The study of noted conductor Pierre-André Valade reading and rehearsing Grisey’s Quatre chants pour franchir le seuil for a 2006 concert with the Ensemble InterContemporain aims at sketching an accurate picture of the preparation of one particular performance. We set up a methodological framework based on cognitive ergonomics and activity analysis, relying on the conductor’s pre-reflective consciousness of his acts, thoughts, emotions, attentional foci before, between and during the rehearsals. The fine-grained data on his course of action/cognition allow to describe it as a chain of “in-formative” (i.e. “shaped from inside”) interactions between him and his environment (including the score and the orchestra). Three notions are emphasized: “anticipation structure,” “the referential,” as well as “appropriations” of several kinds.