For many years the spotlight in drug discovery has been on a relatively small number of validated therapeutic target classes, such as G-protein coupled receptors and enzymes such as protein kinases, with well characterized enzymatic and cellular activities. However, with recent progress in genomics and proteomics, protein-protein interactions (PPIs) provide new way of finding novel bioactive molecules acting on their interfaces. This review addresses the current case studies and state of the art in the development of small chemical modulators controlling interactions of proteins that have pathological implications in various human diseases and in particular in cancer. The attention is focused on Bcl-2 family protein modulators ranging from natural products to synthetic ones with particular interest in foldamers as BH3 alpha helix mimetics.