Electromagnetic (EM) metamaterials have become a field of intense research activities. This paper presents a critical perspective of the field, with emphasis on fundamental concepts and practical applications. Metamaterials are explained in the general context of periodic structures. Resonant particle type and transmission line type metamaterials are compared, and their fundamental connection is established. Exotic phenomena recently reported and associated challenges are briefly reviewed. Practical applications are enumerated and illustrated by an example. The paper concludes with an optimistic outlook regarding the future of metamaterials.

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DOI: 10.1016/S1369-7021(09)70071-9