**Abstract**

The oral drug delivery is widely used and accepted routes of administration, but it fails to provide the therapeutic effectiveness of drugs due to low solubility, poor compression and oral bioavailability. Crystal engineering is the branch where the modification of API is of great importance. Co-crystallization of API using a co-former is a hopeful and emerging approach to improve the performance of pharmaceuticals, such as micromeritic properties, solubility, dissolution profile, pharmacokinetics and stability. Pharmaceutical co-crystals are multicomponent systems in which one component is an active pharmaceutical ingredient and the others are pharmaceutically acceptable ingredients that are of GRAS category. In multidrug co-crystals one drug acts as API and other drug acts as coformer. This chapter illustrates the guidance for more efficient design and manufacture of pharmaceutical co-crystals with the desired physicochemical properties and applications.

**Keywords:** co-crystals, physicochemical properties, characterization, evaluation, drug delivery
