The cucurbit[n]uril (CB[n]) family is an emerging class of host molecules in the field of supramolecular chemistry with a relatively short history (except for CB[6]). The internal cavities of CB[n]s are nonpolar and hydrophobic, guarded by two carbonyl-laced portals, thus they can encapsulate not only neutral molecules via hydrophobic effects but also complex cationic species via ion-dipole interactions. Due to these unique properties, many promising discoveries of supramolecular interactions between CB[n]s and biomolecules and small organic drug molecules have emerged with potential implications in the field of pharmaceutical sciences, which have become one of the most significant areas of potential applications for CB[n]s. In this chapter, we summarize the noncovalent interactions of peptides, proteins and drug molecules with CB[n] homologues and derivatives and discuss the ability of CB[n]s to modulate the functions and bioactivities of these species through host-guest chemistry, as well as the potential of CB[n]s for protein enrichments, together with other relevant topics.