Metamaterials provide the ability to design material properties beyond those possible with conventional materials. Research programs at ONR and other agencies are pursuing fundamental and applied goals with the aim of mapping out the potential of metamaterials for a variety of applications. These programs have pursued optical, RF and acoustic materials for applications across the electromagnetic spectrum, from novel RF antennas to devices utilizing optical magnetism. Acoustic metamaterials are of unique interest to the Navy for underwater applications. Common challenges associated with loss, bandwidth, and scalability will be discussed along with the needs for innovative designs, materials, and fabrication approaches.