Molecular modelling can help reduce the time and risks of drug development. It is applied to target structural characterization, developing focused libraries for hit discovery, and lead development and optimization. Fragment-based drug design is an important advance, where drug candidates are built inside the target's binding site using small molecule fragments to improve affinity from micromolar to millimolar to nanomolar levels. Molecular modelling supports medicinal chemistry decisions by providing structural insights into how drug candidates interact with their targets.