A taxonomy of cocrystal ternary phase diagrams is presented. It is based upon an enumeration of distinct ternary phase diagrams as functions of the free energy of formation for each of a selected set of crystalline phases. In addition to topologically distinct diagrams, phase diagrams are distinguished as to the congruent or incongruent dissolution of the cocrystalline phase. The diagrams are organized according to the set of solid phases and the number of three-phase regions. Phase diagrams and free energy surfaces are provided for representative examples of each illustrated case.