Defence date: 11 March 2016Examining Board: Prof. Árpád Ábrahám, EUI, Supervisor; Prof. Luisa Lambertini, École Polytechnique Fédérale de Lausanne (EPFL); Prof. Evi Pappa, EUI; Prof. Jaume Ventura, CREI and Barcelona GSE.This thesis studies how frictions shape macroeconomic outcomes and affect policies. The thesis consists of three chapters. The first chapter studies how distortionary taxation and volatile output together with government discretion shape sovereign debt issuance and sovereign defaults. It is a novel theory to explain why sovereigns borrow on both domestic and international markets and why defaults are mostly selective (on either domestic or foreign investors). The model matches business cycle moments and frequencies of diffe...