‘Posthumanism’ has become an increasingly visible term over the past decade or so, both within the academy and more broadly. However, as it encompasses a great range of ideas and issues, it can be hard to define what it actually is. In many ways, this heterogeneity lies at posthumanism’s conceptual core—a gathering of intellectual perspectives that share as a basic tenet the belief that the human subject should not be regarded as a stable or bounded substance with ontological primacy over other beings/things, but rather a decentred phenomenon constituted within immanent networks or flows (a general theoretical position often referred to as a ‘flat ontology’). In this contribution, we review the debate on posthumanism as it has occurred within the broader academy before exploring its archaeological implications. This article introduces a volume which continues the Archaeological Review from Cambridge’s engagement with cutting-edge theory in archaeology.