As engineering materials, metamaterials (MMs) have gained a tremendous attention due to their unusual and unnatural electromagnetic responses such as negative refraction and reversed Vavilov-Cerenkov radiation. Electromagnetic characterization of MMs at microwave frequencies is an indispensable key tool in understanding and interpreting the response of the designed MM structures at microwave frequencies in various applications such as perfect lens, electromagnetic cloaks, sensors, and antenna directivity enhancement. The aim of this review is to present some techniques for accurate electromagnetic characterization of bi-anisotropic MM slabs under three important cases: (a) the coupling between electric and magnetic fields is present, (b) the MM structure is a composite inhomogeneous structure constructed by cascade connection of identical or different MM slabs, and (c) the coupling occurs between nearby MM slabs. Simulations and measurements are presented to understand the coupling mechanism between near MM slabs.