This chapter outlines some of the intellectual currents that have led to the development of contemporary critical posthumanism(s). Critical posthumanist thought aims to abandon the essentialisms of humanism and to theorize a human subject constituted not by self-sameness but by difference, not fixed but in process, and entangled in human, non-human, and technological relations. I trace some of the challenges to humanism posed by the antihumanisms of the nineteenth and twentieth centuries, and then offer an overview of some recent and positive philosophical and cultural responses to these challenges, including new ways to think about embodiment and materiality, about our embeddedness in and dependence on the non-human world, and about our simultaneous and globalized entanglement in the cultures of technology. If nothing else, the imminent threat of the climate crisis demonstrates the pressing need to rethink ourselves in/and the world.