Аннотация:In this chapter, we present the basic theory ofMI waves.We start in Section 36.2 with the magnetic coupling between two elements. We proceed with infinite lattices in Section 36.3 and finite arrays in Section 36.4. We aimed here at covering a wide range of topics concerned with MI waves introducing concepts possibly briefly.Those looking for details are encouraged to resort to original publicationswhose list is given at the end of the chapter. This chapter is followed by Chapter 14 of the second volume where we discuss potential applications of MI waves for signal guiding and processing, subwavelength imaging and focusing, detection and amplification of weak signals in magnetic resonance imaging.