Scanning Microwave Impedance Microscopy (sMIM), a new electrical measurement mode for AFM, has shown significant success in the imaging and characterization of electrical properties at 10's of nm length scales. We review the state of the art, including imaging studies revealing electrical characteristics of novel materials and nanostructures, such as composites, graphene, patterned optical crystals and ferro-electrics. The technique is suited for a variety of metrology applications where specific physical properties are determined quantitatively. Examples include the measurement of dielectric constant (permittivity) and conductivity. These capabilities will be presented, illustrating sensitivity and resolution for dielectric constant, doping levels and capacitance.