Nature Materials, Published online: 03 June 2026; doi:10.1038/s41563-026-02601-xRecent developments in in situ micro- and nanoscale mechanical characterization, equipped with exceptional spatial and temporal resolution, are expanding frontiers in the study of functional materials, whose properties are largely defined by their nano- and microscale features. This Review presents a comprehensive overview of these characterization methods and highlights their applications in low-dimensional and architected materials.