Strong emergence means that some things are beyond current physics. This could happen in various ways. A higher level feature could have genuine causal power and violate physical causal closure. Or it could affect the lower level by exploiting unknown physics or the causal slack left by the indeterminism of quantum physics. Or particular configurations of matter could evoke something that is non-physical. There is no logical reason to exclude any such hypotheses, but this chapter argues that neither is there any convincing empirical or theoretical evidence which makes them worth entertaining.