Standard optimal Debt Management (DM) models prescribe a dominant role for long bonds and advocate against issuing short bonds. They require very large positions in order to complete markets and assume each period that governments repurchase all outstanding bonds and reissue (r/r) new ones. These features of DM are inconsistent with U.S. data. We introduce incomplete markets via small transaction costs which serves to make optimal DM more closely resemble the data : r/r are negligible, short bond issuance substantial and persistent and short and long bonds positively co-vary. Intuitively, long bonds help smooth taxes over states and short bonds over time. Solving incomplete market models with multiple assets is challenging so a further contribution of this article is introducing a novel computational method to find global solutions.

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In the context of a sticky price DSGE model subject to government expenditure and preference shocks where governments issue only nominal non-contingent bonds we examine the implications for optimal inflation of changes in the level and average maturity of government debt. We analyse these relationships under two different institutional settings. In one case government pursues optimal monetary and fiscal policy in a coordinated way whereas in the alternative we assume an independent monetary authority that sets interest rates according to a Taylor rule and where the fiscal authority treats bond prices as a given. We identify the main mechanisms through which inflation is affected by debt and debt maturity (a real balance effect and an implicit profit tax) and also study additional channels through which the government achieves fiscal sustainability (tax smoothing, interest rate twisting and endogenous fluctuations in bond prices). In the case of optimal coordinated monetary and fiscal policy we find that the persistence and volatility of inflation depends on the sign, size and maturity structure of government debt. High levels of government debt do lead to higher inflation and longer maturity debt leads to more persistent inflation. However even in the presence of modest price stickiness the role of inflation is minor with the majority of fiscal adjustment achieved through changes in taxes and the primary surplus. However in the case of an independent monetary authority where debt management, monetary policy and fiscal policy are not coordinated then inflation has a much more substantial and more persistent role to play. Inflation is higher, more volatile and more persistent especially in response to preference shocks and plays a major role in achieving fiscal solvency.

We are indebted to Albert Marcet, Chris Pissarides, and especially Rachel Ngai for their continuous support and guidance. We also benefited a lot from the comments of Francesco Caselli, Alex Michaelides, Andreas Müller participants at the LSE Macro Workshop, the XV workshop on Dynamic Macroeconomics in Vigo, the German Economic Association meeting in Kiel, the European Workshop in Macroeconomics in Munich, and also participants in seminars at the HEC Montreal, the

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