This thesis consists of three papers on monetary policy. The first analyzes how endogenous imperfect exchange rate pass-through affects inflation targeting optimal monetary policies in a New Keynesian small open economy. The paper shows that an inverse relation exists between the pass-through and the insulation of the economy from foreign and monetary policy shocks, and that imperfect pass-through tends to decrease the variability of the terms of trade. The second paper focuses on optimal monetary policy in presence of uncertainty of the structural parameters in an open economy. Comparing CPI and domestic inflation targeting, it shows that the latter implies considerably less variability in the distribution forecast of the economic dynamics. The third paper argues that estimated linear monetary policy rules are weighted averages of the actual rules working in the diverse monetary regimes, where the weights merely reflect the length and not necessarily the relevance of the regimes