This paper explores the fundamental ideas that have motivated the idea of emergence and the movement of emergentism. The concept of reduction, which lies at the heart of the emergence idea is explicated, and it is shown how the thesis that emergent properties are irreducible gives a unified account of emergence. The paper goes on to discuss two fundamental unresolved issues for emergentism. The first is that of giving a “positive” characterization of emergence; the second is to give a coherent (...) explanation of how “downward” causation, a central component of emergentism, is able to avoid the problem of overdetermination. (shrink)