A groundbreaking look at Gaia theory’s intersections with neocybernetic systems theory Often seen as an outlier in science, Gaia has run a long and varied course since its formulation in the 1970s by atmospheric chemist James Lovelock and microbiologist Lynn Margulis. Gaian Systems is a pioneering exploration of the dynamic and complex evolution of Gaia’s many variants, with special attention to Margulis’s foundational role in these developments. Bruce Clarke assesses the different dialects of systems theory brought to bear on Gaia discourse. Focusing in particular on Margulis’s work—including multiple pieces of her unpublished Gaia correspondence—he shows how her research and that of Lovelock was concurrent and conceptually parallel with the new discourse of self-referential systems that emerged within neocybernetic systems theory. The recent Gaia writings of Donna Haraway, Isabelle Stengers, and Bruno Latour contest its cybernetic status. Clarke engages Latour on the issue of Gaia’s systems description and extends his own systems-theoretical synthesis under what he terms “metabiotic Gaia.” This study illuminates current issues in neighboring theoretical conversations—from biopolitics and the immunitary paradigm to NASA astrobiology and the Anthropocene. Along the way, he points to science fiction as a vehicle of Gaian thought. Delving into many issues not previously treated in accounts of Gaia, Gaian Systems describes the history of a theory that has the potential to help us survive an environmental crisis of our own making.