This book is a snapshot of the vision shared by outstanding scientists on the key theoretical and experimental issues in Mesoscopic Physics. Quantum properties of electrons in solid state devices and transport in semiconducting and superconducting low-dimensional systems, are discussed, as well as the basis of quantum computing (entanglement, noise decoherence and read-out). Each chapter collects the material presented at a Varenna School course of last year, by leading experts in the field. The reader gets a flavour of how theorists and experimentalists are paving the way to the physical realization of solid state qubits, the basic units of the new logic and memory elements for quantum processing. He will be surprised in finding that mesoscopic solid state devices, which were invented only yesterday (think of the Single Electron Transistor, or the Cooper Pair Box) are currently used as charge-sensing applications in the equipment of frontier research laboratories. These devices contribute as probing systems to produce evidence on still unsettled questions in topics like the metal-insulator transition in disordered two dimensional systems, quantum Hall conductance in heterostructur"