Being a strong β stabilizer, Mo has gained importance as an alloying element for so-called β/γ-TiAl alloys. Intermetallic TiAl-based alloys which contain a significant volume fraction of the body-centered cubic β-phase at elevated temperatures have proven to exhibit good processing characteristics during hot-working. Unfortunately, the effect of Mo on the appearing phases and their temperature dependence is not well known. In this work, sections of the Ti-Al-Mo ternary phase diagram derived from thermodynamic calculations as well as experimental data are presented. The phase transition temperatures stated in these phase diagrams are compared with the results of high-temperature diffraction studies using high-energy synchrotron radiation. Additionally, the disordering temperature of the βo-phase is determined.