Diversity-oriented synthesis has historically focused on the generation of small-molecule collections with considerable scaffold, stereochemical, and appendage diversity. Recently, this focus has begun to shift to the production of small-molecule libraries with diverse biological activities. It is currently not clear which properties and structural features of molecules are predictive of diverse performance in biological assays, and a better understanding of this relationship is critical for the development of performance-diverse small-molecule libraries for the discovery of novel probes for challenging targets. This review explores recent synthetic strategies for the production of bioactive small molecules and concludes with a presentation of current methods that enable the assessment of the biological performance diversity of small-molecule libraries.