This book argues that, by virtue of his original and ongoing contribution to ontology and modal philosophy (from the texts gathered inPsychanalysis and Transversality to the unpublished manuscript notes forWhat Is Philosophy?), Guattari is to be acknowledged a philosopher in his own right, independently from Deleuze. Furthermore, it looks back and forth beyondAnti-Oedipus and contends that Guattari’s major writings gradually supplement deterritorialization with determinability. Accordingly, it offers a new interpretation of the nuanced development of Guattari’s philosophical thought, which it proposes to define as constructivist, rather than post-structuralist. Additionally, it explores the innovative responses that Guattari’s philosophy supplies to various contemporary philosophical debates like those on accelerationism, indeterminacy, compossibility, and worlding. Finally, it examines the differences that, upon a careful cross-reading of their earliest texts (includingThe Anti-Oedipus Papers and Difference and Repetition), must be drawn between Guattari’s constructivism and Deleuze’s sacrificial philosophy.