Alternative currencies are means of payment that circulate alongside—as an alternative or complement to—official currencies. While these currencies have existed for a long time, both society and academia have shown a renewed interest in their potential to decentralize the governance of monetary affairs and to bring people and organizations together in more ethical or sustainable ways. This article is a review of the ethical and philosophical implications of these alternative monetary projects. We first discuss various classifications of these currencies before analyzing the ethical challenges linked to the way they tackle social and environmental issues. We also examine the incentive-based and coercive mechanisms used by these currencies from an ethical perspective and debate the promises and perils of monetary decentralization and democracy. We conclude by identifying an agenda for future research.