Laser Doppler Velocimetry technique is used by many experimentalists to obtain accurate velocity measurements in a wide range of flows. The accuracy of the rate at which measurements are obtained depends directly on the system performance. One of the key elements affecting the performance of an LDV system is the source of the Doppler signal—the scattering particles in the flow. Although the first reaction of many users is to rely on particles naturally present in the flow, it is desirable to seed the flow to obtain adequate data rates and good signal quality. Generally, no systematic approaches are used or only very little attention is paid to the proper selection of the particles. The requirements of seed particles for successful LDV measurements can be summarized as: small enough to follow the flow and large enough to generate sufficient scattered light. However, translating this into actual physical properties is a complex and confusing problem. This paper will examine these general requirements in a detailed and systematic manner. The source for the signal in LDV is the scattering particle. Geometric and physical parameters of the particles influence the quality of the signals obtained from the photodetector of an LDV system. Although the first reaction of most experimenters is to rely on particles naturally present in the flow, it is desirable to seed the flow to obtain adequate measurement rates and good signal quality. There are only a few situations (e.g., forward-scatter in water) where the particles naturally present are adequate to provide good measurements. The proper choice of seed material can significantly improve the performance of an LDV system. The guideline for selection can be summarized as the particles should be small enough to faithfully follow the flow and large enough to “generate” sufficient scattered light intensity. However, translating this into actual physical properties involves compromising conflicting requirements. Hence, often very little attention is paid to the proper selection of the particles. The fact that no single physical parameter describes the light-scattering ability has made it difficult to come up with the optimum seed particle. In addition, aspects such as number concentration, ability to survive the environment, and toxicity also influence the choice of seed material. The signal quality or signal-to-noise ratio (SNR), quantifies the LDV system performance and hence, needs to be maximized to obtain maximum flow information accurately. Various aspects relating to the choice of seed particles follows. The way the particles are dispersed depends on the type of flow. In general, atomizers are used to generate droplets from liquids or particles suspended in liquid medium. If particles are available as dry powder, they generally can be dispersed using fluidized bed generators. Various methods of generating aerosol seeding have been discussed in References 3 and 4.