We propose three essays on the evaluation of the recent measures undertaken by many central banks that go under the name of unconventional monetary policy. In particular, we focus on Large Scale Asset Purchases (LSAP), often referred also as Quantitative easing (QE), texploring the so called portfolio rebalance channel of transmission, that exploits the imperfect substitutability of financial assets and affects the economy through the longer term interest rates. The thesis is structured in three chapters. The first chapter presents a review of the main works that try to assess the effects of unconventional policies both from an empirical and a theoretical point of view. In particular, in the first part we describe the main contributions to...