This chapter links the basic principles of magnetic resonance with the relevant hardware components in a magnetic resonance system. These components include the magnet, radiofrequency coil(s), radiofrequency amplifier, shim coils, magnetic field gradient coils, gradient amplifiers, frequency locking circuitry, and receiver. The role of each component is explained in terms of its relationship to the associated magnetic resonance phenomenon, e.g. nuclear polarization, resonance frequency, precession, the effect of radiofrequency pulses, relaxation and spatial encoding. The requirements of each of the hardware components are quantified for experiments in three different “domains”: high-resolution liquid-state nuclear magnetic resonance spectroscopy, magic-angle spinning solid-state nuclear magnetic resonance spectroscopy, and magnetic resonance imaging. Finally, an Appendix is included, which contains details of two mathematical frameworks, namely spherical harmonics and the Biot–Savart law, used in the design of magnets, shim coils, magnetic field gradients and RF coils throughout the book.