In recent years, density-functional theories have been widely used in treatments of electronic problems, ranging from small molecules to solids.  But density- functions, in some form or other, have been used in other endeavors before, in particular, in the treatment of intermolecular forces and also in the development of thermodynamic potentials. This paper reviews the salient points of the theory of intermolecular forces, obtained on the basis of the reaction-potential approach and formulated in terms of charge-density and charge-density susceptibilities (or non-local polarizabilties). The treatment is illustrated by application to rotationally averaged intermolecular forces of polar molecules, and formulations for electrostatic, polarization and dispersion interactions are discussed in some detail. Finally, the formalism is generalized to include translational interactions and a unified treatment is presented of intermolecular and thermodynamic potentials of fluids. The latter is expressed   in terms of   molecule-density expectation values, molecule-density susceptibilities and intermolecular potentials. It is shown that for a classical fluid, the free energy is consistent with the standard statistical mechanical formulation within the RPA (random phase) approximation.