The solubility behavior of salicylic acid (SAA)/4,4'-dipyridyl (4,4'-dipy) cocrystals is investigated in an ethanol solvent. The phase solubility diagram (PSD) of SAA/4,4'-dipy cocrystals is determined which are formed in a 2: 1 stoichiometric ratio in ethanol. The objective is to improve the fundamentals of the formation mechanisms, solution behavior, and solid-state properties of SAA/4,4'-dipy cocrystals. The solubility behavior and solution chemistry of cocrystals are studied. It was found that the thermodynamic stability regions of the cocrystals and its components are defined by the phase solubility diagram. Besides the kinetic also the thermodynamic factor turned out to be important for the crystallization of cocrystals.