This chapter provides a brief historical introduction to quantum theory, and shows that the theory opens up some radically new ways of thinking about the place of mind and consciousness in nature. Quantum theory is all about learning, on the basis of scientific experiments, to question the "obvious" truths about the nature of the physical world and to come up with more coherent alternatives. The chapter considers the famous two-slit experiment. It explores what the different interpretations of quantum theory say about situations like the two-slit experiment, and also considers what kind of theories of mind and consciousness some interpretations have inspired. The attempt to explain mind and consciousness in terms of the quantum theory involves heavy speculation. The advances in quantum biology, while not giving direct support to quantum brain theory, perhaps make a biologically grounded quantum theory of consciousness seem less inconceivable.