Metrology is the science of measurement and its application. It is essential for characterizing microsystems and structures below what can be perceived with the naked eye. Key metrology tools for microscale include optical microscopy, scanning electron microscopy, atomic force microscopy, interferometry, and ellipsometry. These tools allow measuring parameters like length, thickness, roughness, composition, and defects at micro- and nanoscales. Statistical analysis is also important in metrology for understanding measurement uncertainties and variations.