Much research on complementary currencies (CCs) focuses on the social, political and cultural determinants of their emergence and success or failure. Less attention is placed upon economic and monetary theory itself when studying CCs. Yet, the financial crisis has made clear the weakness of existing monetary theory and policy. Despite this, few alternatives have emerged. Orthodox monetary theory and policy, based upon hypothetico-deductive models of the economy which do not resemble reality and where money is viewed as of no significance as a policy instrument, remain dominant. In contrast, CCs absolutely reject the neutrality of money argument and can be seen as experiments in building the ‘monetary networks’ that are the basis of any monetary system, including orthodox credit-money. Two case studies are used as examples to highlight theoretical insights that can be derived from inductive empirical research on CCs – in this case the Brixton Pound and the Swiss WIR. Both systems challenge elements of mainstream monetary theory, reveal the socially and politically constructed nature of money and raise significant questions for further research. The article concludes by advocating rigorous empirical research on CCs with a stronger focus on filling out many of the gaps in existing monetary theory.