The Al-Cu binary system has been investigated intensively in the past as key binary system for many important industrial alloys. With respect to new experimental results about phase equilibria in Al-Cu system, it was found necessary to prepare new CALPHAD-type thermodynamic description of the Al-Cu system. In course of this work, the known crystallography of several intermetallic phases and the information about site occupations in particular crystallographic positions were implemented in the new thermodynamic phase descriptions. The intermetallic phases were furthermore modelled with all their different temperature modifications. Very good agreement with the experimental results was reached both, for the Al-Cu phase diagram and for the calculated thermodynamic properties, namely the enthalpy of mixing, enthalpies of formation and thermodynamic activities.