|Recently, metamaterials have attracted considerable attention due to their feasibility and multiple applications. As man-made artificial structures, metamate-rials possess properties that are not yet highlighted in the natural world, such as perfect lensing, negative refraction, and backward propagation. These properties are obtained by the proper design of the structure of metamaterials, with the periodic arrangement of unit cells, ”meta-atoms”, which have dimensions below the order of magnitude of the inci-dent wavelength, at which resonance processes can be estab-lished. Thus, the electric and magnetic response of the met-amaterial can be flexibly tailored to meet the desired macro-scopic properties, in terms of effective electric permittivity and magnetic permeability. In this paper, a review of the state of research and development of metamaterials is made, highlighting the new challenges and ways to improve and to apply these new synthetic structures in electromagnetics and optics. There are analyzed the processes and structures of metamaterials used in various applications. Based on the actual researches, new classification of metamaterials with the criterion of the capabilities and flexibilities in controlling electromagnetic waves is described and analyzed.