The conceptual foundations of quantum mechanics The book starts with a description of classical mechanics then discusses the quantum phenomena that require us to give up our commonsense classical intuitions. We consider the physical and conceptual arguments that led to the standard von Neumann Dirac formulation of quantum mechanics and how the standard theory explains quantum phenomena. This includes a discussion of how the theorys two dynamical laws work with the standard interpretation of states to explain determinate measurement records quantum statistics interference effects entanglement decoherence and quantum nonlocality. A careful understanding of how the standard theory works ultimately leads to the quantum measurement problem. We consider how the measurement problem threatens the logical consistency of the standard theory then turn to a discussion of the main proposals for resolving it. This includes collapse formulations of quantum mechanics like Wigners extension of the standard theory and the GRW approach and no collapse formulations like pure wave mechanics the various many worlds theories and Bohmian mechanics. In discussing alternative formulations of quantum mechanics we pay particular attention to the explanatory role played by each theorys empirical ontology and associated metaphysical commitments and the conceptual trade offs between theoretical options