The modification of solid-state properties of active pharmaceuticals ingredients (APIs) in the market show poor physicochemical properties, mainly solubility and stability, and this poses serious problems for clinical development and can lead to late stage drug failure. Improving the solubility and bioavailability of poorly water-soluble drugs is a difficult challenge for pharmaceutical scientists. In addition to salts and cocrystals, other techniques such as micronization, micellar solution, oil encapsulation, and amorphous phase by means of solid dispersions by using polymers, cyclodextrins, and additives have been widely used.However, salt formation and cocrystallization of the API are the first-choice methods to improve the solubility and bioavailability of poorly soluble drugs using crystal engineering principles without changing their chemical structure. Salt formation is a preferred method to improve physicochemical properties because it makes the drug molecule ionized, and furthermore, other favorable factors, such as high melting point, crystallinity, filtration, stability, etc., are also optimized in salts.