A review of the theoretical principles underlying electromagnetic induction in the Earth is provided. The discussion is based on the magnetoquasistatic (MQS) formulation of the pre-Maxwell equations wherein electromagnetic diffusion prevails while capacitive and wave effects are completely neglected. The electromotive force and mutual inductance of flux-linked conductors emerge as key concepts. Some interesting, counter-intuitive and otherwise surprising implications of the MQS approximation are presented. Mention will also be made of boundary conditions, analogies to heat transport, and the flow of electromagnetic energy via the Poynting vector.