Introduction and overview -- The early development of coins and paper currency -- Size and composition of global currency supplies, and the share held abroad -- Holdings of currency in the domestic legal, tax-paying economy -- Currency demand in the underground economy -- Seigniorage -- A plan for phasing out most paper currency -- The cost of the zero bound constraint -- Higher inflation targets, nominal GDP, escape clauses and fiscal policy -- Other paths to negative interest rates -- Other possible downsides to negative nominal policy rates -- Negative interest rates as a violation of trust and a step away from rule-based systems -- International dimensions to phasing out paper currency -- Digital currencies and gold -- Final thoughts.