Metamaterial is a kind of artificially structured material with optical properties that cannot be found in nature. This presentation covers the recent advances in the study of plasmonic metamaterials ranging from fundamental aspects to up-to-date applications. Special emphasis will be given on the new frontier of the metamaterial/plasmonic research, where nonlinear and quantum effects emerge together. 1. I will introduce an efficient model to describe the nonlocal and quantum nature of metallic electrons and show how the nonlocal effects can be used to enhance the nonlinear responses of plasmonic metamaterials; 2. I will show how judiciously structured metal surfaces can help transfer distinct properties of optical plasmons to much lower frequencies with greatly suppressed plasmonic losses. Based on this concept, I will discuss our recent experimental developments on spoof-plasmon-enabled invisibility dips and backward phase matching in nonlinear spoof plasmon waveguide.