Spray Systems are used very extensively in a wide range of industrial applications. Injection of liquid fuel in gasoline and diesel automotive engines, gas turbine aircraft and land-based engines, rocket engines and a wide variety of industrial furnaces and boilers, require improved control of atomization and spray characteristics to improve performance and efficiency and to reduce emission of pollutants to satisfy EPA regulations. Spray painting of automobiles, aircraft, bridges and a large range of manufactured products results in the waste of large proportions of paint that does not hit the target and is carried away by offspray, which requires expensive treatment to prevent pollution. In manufacturing processes, molten metal sprays are used for direct manufacture, using near net shaping, high temperature arc spray coatings (thermal spraying) and for coatings. The need to achieve uniform thickness film layers with low porosity, requires control of drop size, velocity, temperature and number density in the spray. More than 80% of agricultural crops are sprayed with herbicides, fungicides and insecticides, using aircraft and tractors. Drop size needs to be maintained sufficiently large during evaporation to prevent drift by wind away from the target crop. Drops that are too large cause wastage and low target transfer efficiencies. Control is required of initial drop size distributions and subsequent changes of spray characteristics from nozzle to target crops. Many industrial chemical and food processes use spray drying where liquid slurries, colloids and solutions are injected into heated gas (air) environments. Control of atomization and spray characteristics is required in order to meet the end product specifications, of particle size, agglomeration, porosity and friability. In the field of medicine, inhalation therapy is used for treatment of respiratory diseases. New developments include inhalation of cyclosporin to prevent rejection after lung transplants, deep lung inhalation of insulin as a more effective and comfortable treatment for diabetics and inhalation of chemotherapy for prevention of lung cancer for heavy smokers. The generation of monosize particles in nebulizers targeted to particular locations in the respiratory tract and lung surfaces requires accurate control of particle size and velocity during inhalation. Control of all these spray processes is achieved by improved atomizer design and accurate measurement of spray characteristics by phase Doppler, diffraction and imaging laser diagnostic instruments.