This chapter provides a philosophical framework for the rest of the book. Emergence is closely linked to the idea that the world is divided into levels, with higher levels emerging from lower ones. Once the concept of levels is clarified, the chapter turns to Jaegwon Kim’s argument that emergence is either an empty concept or must contradict physics. The argument can be stated as six propositions of which only a maximum of five can be true. The choice of which proposition to reject corresponds to a way of seeing the world: dualism, three types of physicalism, weak emergence and strong emergence.