Medicinal chemistry research has traditionally focused upon a limited set of biological targets. Many other human disease-related targets have been termed ‘undruggable’ as they have proved largely impervious to modulation by small molecules. However, it is becoming increasingly evident that such targets can indeed be modulated; they are simply being challenged with the wrong types of molecules. Traditionally, screening libraries were composed of large numbers of structurally similar compounds. However, library size is not everything; the structural diversity of the library, which is largely dictated by the range of molecular scaffolds present, is crucial. Diversity-oriented synthesis (DOS) generates small molecule libraries with high levels of scaffold, and thus structural, diversity. Such collections should provide hits against a broad range of targets with high frequency, including ‘undruggable’ targets. Examples in the area of scaffold diversity generation taken from the author’s laboratories are given.