The monograph presents the results of studies of aerohydrodynamic effects resulting from the interaction of a gas jet with the surface of a viscous fluid. The ways of search of scientific and technical solutions directed to creation of fundamentally new contactless inkjet pneumatic methods and means of non-destructive control of viscosity of liquids are defined. Peculiarities of measurements of viscosity of moving liquids, as well as liquids under conditions of elevated temperatures are considered. Descriptions of contactless methods and their implementing devices providing the measurement of viscosity of liquid substances both outside and inside technological devices. are given. The monograph can be useful to specialists engaged in the development and operation of highly reliable methods and devices for controlling substances in various industries.