Metamaterials offer the possibility to control and manipulate electromagnetic radiation. Spoof surface plasmon metamaterials are the focus of this Element of the Metamaterials Series. The fundamentals of spoof surface plasmons are reviewed, and advances on plasmonic metamaterials based on spoof plasmons are presented. Spoof surface plasmon metamaterials on a wide range of geometries are discussed: from planar platforms to waveguides and localized modes, including cylindrical structures, grooves, wedges, dominos or conformal surface plasmons in ultrathin platforms. The Element closes with a review of recent advances and applications such as Terahertz sensing or integrated devices and circuits.