Preface 1 Introduction 1.1 Magnetism and Other Effects of Electron-Electron Interaction 1.2 Sources of Magnetic Fields 1.3 Getting Acquainted: Magnetite 1.3.1 Charge States 1.3.2 Spin States 1.3.3 Charge Ordering 1.4 Variety of Correlated Systems: An Outline of the Course 2 Atoms, Ions, and Molecules 2.1 Hydrogen Atom in a Magnetic Field 2.1.1 Non-Relativistic Treatment Motion in a Magnetic Field Zeeman Effect (I) 2.1.2 Relativistic Effects Spin-Orbit Coupling Zeeman Effect (II) Problem 2.1 2.2 Direct Exchange Problem 2.2 2.3 Many-Electron Ions Problem 2.3 2.3.1 Coupling to the Magnetic Field Digression: The Bohr-Van Leeuwen Theorem ……