Shanming Kuang Center for Pharma Crystallization, J-Star Research Inc 6 Cedar Drive, Cranbury, New Jersey 08512 shanming.kuang@jstar-research.com Abstract Rational selection of solvents plays a critical role in solid form screening and production. On the one hand, a variety of solvents with different properties are chosen in form screening to maximize the screening space of searching for all potential solid forms because some solvents selectively favor the generation of a particular form as a result of crystallization kinetics. On the other hand, some solvents need to be avoided in crystallization process due to formation of solvates that result in issues in residue solvent control and/or form transformation. We will present a lesson learned from a case study in which the wrong solvent was selected, which created huge pain in the commercialization. Efforts including computational approach utilized to address this issue will also be discussed.