Co-crystal formation is one of the methods to improve the physico-chemical properties of the active pharmaceutical ingredient. Co-crystallization with pharmaceutically acceptable compounds do not affect the pharmacological activity of the API but can improve physical properties such as solubility, dissolution rate, moisture stability and compaction behavior. Co-crystals are most dynamically developing group of multicomponent solid pharmaceutical substances. Co-crystals can be divided into co-crystal anhydrates, co-crystal hydrates (solvates), co-crystals of salts (unsolvated, unhydrated, solvated or hydrated). Techniques for preparation of co-crystals are solvent evaporation, anti-solvent method, hot melt extrusion and solvent free grinding. Co-crystals are characterized by hot stage microscopy, differential scanning calorimetry, X-ray diffraction, IR and Raman spectroscopy.