Traditional metamaterial engineering has predominantly focused on the spatial arrangement of meta-atoms. While spatial metamaterials can achieve effects not found in nature, their performance remains constrained, unable to fully unlock their potential. Recently, time has emerged as an additional degree of freedom in material design, offering new possibilities to surpass the limitations of purely spatial metamaterials. This session will highlight recent advances in the wave phenomena and underlying physics of time-modulated metamaterials and metasurfaces. Topics will include, but are not limited to, time-varying metamaterials and metasurfaces, photonic time crystals, and space-time modulated structures and components.