The nuclear magnetic resonance (NMR) method has been successfully applied to measure the magnetic moment of various nuclei. The principal feature of this method is the observation of transitions caused by resonance of an applied radio frequency field with the Larmor precession of the moments around a constant magnetic field. This book presents the basic principles of the very important applications of NMR, magnetic resonance imaging (MRI). It has been shown how to obtain the average magnetization of a sample from magnetic moments of nuclei. It is the average magnetization that has to be detected by the detection system to generate an output signal which in turn can be converted to digital data to display image of the sample. This material may be valuable for senior undergraduate students, postgraduate students and junior researchers who are interested in the study of basic sciences and technological applications of NMR.