This chapter introduces readers to numerical dosimetry and computational bioelectromagnetics through a discussion of dosimetric methods involving macro- and microinteractions with human and animal models. In order to understand the effects of electromagnetic fields (EMF) on biological tissues, it is necessary to determine the magnitude of induced electric fields and induced densities in the various parts of the object. The homogeneous human body with a single conductivity was modeled in extremely low–frequency (ELF) EMF. Researchers considered ELF electric fields coupling to prolate and oblate dielectric spheroidal models. The calculations of induced current densities and the electric fields were carried out for these simple human models exposed to a uniform ELF electric or magnetic fields by simple analytical methods. Dosimetric studies in animals exposed to ELF electric fields were conducted jointly by the United States and Japan at the Central Research Institute of Electric Power Industry and the University of Tokushima.