This thesis is constituted by three essays in Monetary Economics. In the first article we built a theoretical model to assess how monetary policy in equilibrium reacts to different agents’ perceptions about Central’s Bank (BC) preferences. We conclude that, at times, Central Banks perceived as more lenient with inflation implement, at equilibrium, more rigorous monetary policy than their peers perceived as more averse to inflation. Therefore, there isn’t a monotonic relation between agents’ perceptions about BC’s preferences and monetary policy in equilibrium. In the second article, we empirically estimate the impact of changes in interest rate expectations on inflation expectations and GDP growth. Likewise, we measure the impact of changes in inflation expectations on interest rate and GDP forecasts. We found that agents believe BC reacts strongly to inflation shocks when inflation forecast is above its target. On the other hand, interest rate expectations are more affected by changes on GDP forecasts when the projected growth is below 3,5%. Finally, on the third essay, we investigate if the disinflation cost in Brazil is motivated by inflation rigidity or price rigidity combined with inflation expectation not fully rational. We concluded that, between 2001 and 2009, there is strong evidence that support the second hypothesis.