The delivery of synthesized drugs exhibiting poor solubility in water is extremely difficult, limiting bioavailability and causing adverse effects when solubilized. A need was determined for developing a formulation to deliver poorly water‐soluble drugs without indiscriminately reaching healthy organs and tissues. Therefore, nanocrystal formulations have been a significant focus for delivering poorly water‐soluble drugs via oral, paraenteral, and alternative routes. Using nanocrystal formulations avoids potential side effects and instability related to many existing delivery systems. Currently, few cancer therapy products are approved by the Food and Drug Administration (FDA) in which poorly soluble drugs are formulated by nanoparticles. In this chapter, the production of nanocrystals of pharmaceutical organic compounds is reviewed. Thereafter, the chapter will focus on the application of nanocrystals for cancer therapy.