The paper presents the literature-based review of phase diagrams for the B2O3-Li2O, B2O3-MoO3, LiO2-MoO3 binary systems and B2O3-Li2O-MoO3 ternary system and the results of the experimental studying the polythermal sections of Li2O .B2O3 -Li2O . MoO3, Li2O . 3B(2)O(3) - MoO3 and Li2O . 3B(2)O(3) -2Li(2)O . 5MoO(3) systems. The section of Li2O .B2O3 - Li2O . MoO3 was confirmed to be quasi-binary: it: divides the ternary phase diagram into two subsystem diagrams, which can be investigated independently. Basing on original and published data the topological analysis of liquidus surface in the B2O3 -Li2O .B2O3 - Li2O . MoO3 subsystem -which is of special interest for the growth of lithium triborate (LBO) single crystals -was performed. Due to the lack of information several topologies of the surface may be provided which accord well with the available experimental data. It was shown that to choose a correct version of topology one could use the data on the subsolidus triangulation of the compositional tetragon of the subsystem under investigation, The relevant experiment was carried out and the triangulation scheme was determined through the phase composition of one sample. The topological scheme of liquidus surface and the subsolidus triangulation scheme in the compositional tetragon of the B2O3 - Li2O .B2O3 - Li2O . MoO3 -MoO3 subsystem were plotted. We succeeded to define the region of LBO primary crystallization on the phase diagram and to grow optically good-quality LBO single crystals.