iSCAT relies on the interference between light scattered from an object of interest supported on a glass coverslip, and reference light reflected back from the same glass-sample interface (Fig. ). Compared to conventional interferometry, the common path agreement of iSCAT provides a simple and robust approach to measure changes in light scattering from small objects. For a diffraction-limited object, iSCAT signals appear as an Airy disc of concentric dark and light rings caused by the interference between the reflected and scattered signals. iSCAT offers lateral and axial resolutions of around 200 -300 nm and 10 -100 nm, respectively, and can further exploit optical super-resolution techniques to improve spatial precision. In addition, iSCAT can operate at high temporal resolutions (up to 1 µs) and monitor processes over long observation times without photobleaching.