Correlated-electron systems offer a unique playground for discovering and studying new quantum states of matter, at the crossway between itinerant quantum magnetism and unconventional superconductivity. The understanding of their basic properties, although needing experimental environments which cannot be transposed at industrial scales, will surely benefit within mid- and long-term perspectives to future revolutionary applications in the domains of applied physics, micro and nano-electronics, energetics.As textbook examples of quantum magnets and unconventional superconductors, heavy-fermion compounds offer a fertile ground for testing new concepts in condensed matter. Quantum magnetic phase transitions can be easily tuned experimentally, leading to a large variety of electronic ground states, from a heavy Fermi liquid to long-range magnetic-order and unconventional superconducting phases. This book written by William Knafo, an expert in correlated-electron physics, proposes a systematic and thorough review on the experimental advances in the study of magnetism in heavy-fermion metals over the last decades. The phase diagrams of these quantum materials under multiple sets of tuning parameters, the questions of the dual localized-itinerant nature of the f-electrons and of the critical role of magnetic fluctuations, in relation with nearby quantum magnetic phase transitions and the stabilization of superconductivity, are carefully addressed.