Some discotic liquid crystals can form stable monolayers at the air-water interface. Depending on their chemical structure two different arrangements of the discs are possible, edge-on and side-on, which crucially influence the mono- and multilayer behaviour. It is found that the rather unpolar triphenylenes prefer monolayers of the edge-on type. The monolayer stability is improved by incorporation of hydrophilic groups into the side group region of the molecules or by polymer fixation. LB multilayers can be formed on solid supports, which show photoconductivity. In contrast, the more polar class of disc-like phloroglucinols show a more complex behaviour at the air-water interface. Depending on the substitution pattern, edge-on or side-on arrangements can occur. On compression beyond the classical collapse point, defined multilayers were obtained at the air-water interface, which were investigated by surface plasmon spectroscopy.