A survey is given of the recent work in the Department of Inorganic Chemistry of the Eindhoven University of Technology on the rheological properties of alkali borate glasses. With the help of a specially adapted viscosimeter the rheological properties of systematically varied series of alkali borate glasses are measured. These include the coefficients of viscosity in the 109–1012 poise region and the corresponding yield values; they are discussed as a function of composition and of the water content of the samples. Conclusions can be drawn about the structure of borate glasses in question and the manner in which the water is built into the network. Whereas relative small amounts of alkali oxides built into the network of B2O3 give rise to boron atoms with a tetrahedral coordination, small amounts of water are taken up by the mechanism of breaking B—O—B bonds.