Pharmaceutical co-crystals have lately been explored as a class of solid phase drugs with enhanced physiochemical properties. The fact that awakens interest in co-crystals is that by preparing active pharmaceutical ingredients (API) by methods of co-crystallization increases the total number of possible crystal forms for already existing APIs. It is also important to note that these methods of API preparation open up new pathways and opportunities regarding intelectual property amongst pharmaceutical companies as well as help enhance their properties, such as: solubility, stability and bioavailability which are of great importance for drug application. In this study, a model system for creating co-crystals; maleic acid and caffeine, was tested. The aim of this study was to generate all existing co-crystal forms of maleic acid and caffeine as well as explore the effect of starting temperature, starting concentration of both components in the solution and ultrasound on the final phase equilibrium. Co-crystals were identified by X-ray diffraction, and characterized through differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Despite the fact that only one case a pure form was isolated, the rest of the results nevertheless gave very good insight regarding the effects of the studied parameters on the possibilities of preparing various co-crystal forms.