I explain the meaning of an interoperable payment system and why interoperability is crucial for efficiency. I review some alternative approaches to interoperability, including central bank digital currencies (CBDCs), hybrid CBDCs, and two-ledger upgrades of bank-based payment systems

Over millennia, mankind has used hard cash in various forms ranging from shells to gold coins and paper. More recently, cash has become unpopular in political circles, as it effectively restricts states’ power to tax (explicitly or via negative interest rates) or to survey and potentially...