This book is intended to provide the basis of knowledge to design and build NMR probeheads specific for a given experiment like in vivo magnetic resonance spectroscopy or imaging. Since the book is intended for practical use, each step leading to the realization of the probe is detailed. The covered subjects include the principles of operation of NMR probes, and guidelines for choosing a specific configuration, as well as the electrical and mechanical details to construct the resonator. Examples of NMR probes, already built and working, are given and commented in detail. A set of tools (formulae and numerical calculations) useful for designing, evaluating and debugging the probes are given.