Optical glass provides a central function in optical systems: the precisely defined refraction of light with the highest throughput. Large parts of the optical industry depend on this key material. Microscopes, binoculars, cameras, and projectors constitute examples that are unthinkable without optical glass. Their properties, however, differ considerably from those of other technical materials such as metals or plastics. Datasheet values of refractive index extend to five decimal places (e.g. 1.51680) and homogeneity might be specified to even two more digits (e.g. 2x10-7). This extreme precision sets optical glass apart from most other materials. For optical glass users it is important to know facts about its production and properties in order to specify optical elements adequately. Engineering drawing requirements must ensure sound function of the optical system but should do so without over-specifying various attributes which might lead to higher costs, delivery time delay, or even non-availability. Application formats extend from the millimeter range up to about one meter. For small parts, glass properties are usually not expected to be critical. Most properties, however, do not scale up linearly with the sample size. For large lenses and prisms, different scaling laws of glass properties must be taken into consideration in order to obtain suitable quality. For designing and purchasing of optical elements it is very useful to know the technical conditions of producing, post-processing, quality inspection, and application of optical glass. This course provides knowledge about glass types and properties, including definitions, tolerances, and measurement methods. Relevant properties to be discussed include refractive index, dispersion, transmission, homogeneity, striae, stress birefringence. Also covered are production processes and their influences on glass properties, raw glass delivery formats. The course covers specification of lenses and prisms for optical systems according to the international standards ISO 10110 (optical elements) and ISO 12123 (raw optical glass). Finally, availability of optical glasses and restrictions thereof due to technical, economic, and regulatory reasons are covered.