This book explores the philosophy and the foundations of quantum chemistry. It features chapters written by experts in the field. The contributions analyze quantum chemistry as a discipline, in particular, its relation with both chemistry and physics from the viewpoint of realism and reduction. Coverage includes such topics as quantum chemistry as an “in-between” discipline, molecular structure and quantum mechanics, quantum chemical models, and atoms and molecules in quantum chemistry. The interest of this book is twofold. First, the contributions aim to update and refresh the discussions regarding the foundations of quantum chemistry. Second, they seek to develop new philosophical perspectives that this discipline can suggest to philosophers of science. From its origins, quantum chemistry filled a problematic position in the disciplinary space. On the one hand, it is a branch of theoretical chemistry. On the other hand, it appeals essentially to theoretical tools coming from physics. This peculiar position triggered conceptual questions about its own identity. Inside this book, readers will find updated discussions on the foundations and the philosophy of this complex discipline.