Rhodanine has been associated with a wide variety of pharmacological activities and has been the target of extensive scientific debate in the past few years. Attention has been focused on the suggested problematic behaviour of compounds containing the rhodanine moiety, following the description by Baell et al. of rhodanines as frequent hitters or pan assay interference compounds (PAINS). The authors suggested, therefore, that rhodanines should be excluded from the compound libraries used for biomolecular screening and provided filters for eliminating such compounds using computational tools. Interest in rhodanines, nevertheless, still remains, with reports of their novel biological activities that highlight the rhodanine moiety as a privileged scaffold in the search for new biologically active compounds. This chapter describes the physicochemical properties and reactivities of rhodanines, followed by discussion about their biological activities, particularly their antibacterial, antiviral and anticancer activities. Finally, we highlight examples of rhodanine-based compounds progressing to clinical studies and use in therapy.