The Quartz Crystal Microbalance with Dissipation Monitoring determines mass change on sensors in situ and in real time. The active component of a QCM-D is a thin quartz crystal disk sandwiched between a pair of electrodes. The application of an AC voltage over the electrodes causes the crystal to oscillate at its acoustic resonance frequency. When the AC voltage is turned off, the decay of oscillation due to the presence of the adsorbed materials on the sensor surfaces is determined by a special data acquisition system. Current QCM-D equipment enables measuring of more than 200 data points per second. By monitoring this decay, the instrument is capable of determining the resonance frequency and the energy dissipation factor. The QCM-D works in situ and in real time without the need of labelling. It is used to study molecular adsorption/desorption, binding kinetics of polymers to various types of surfaces, and deposition of fine particles in sensor surfaces.