While securities exchanges have been facilitating financial market transactions for centuries, the first social stock exchanges were officially launched only recently. These sorts of exchanges aim to connect social enterprises with so-called "impact" investors. Broadly, such an exchange enables private capital to be mobilised for public good. Yet we also need to recognise criticisms of such exchange platforms, as well as unintended consequences. We also need to ensure that mobilising private capital does not lead governments to shirk their responsibilities in dealing with those social and environmental problems that will not be addressed through market mechanisms.