In this thesis, by focusing on the unconventional monetary policy measures, I have analytically assessed post-great moderation central banking policies and documented the heterogeneity in calibration and design of these policies by exposing the experiences of Japan, United States, United Kingdom and Brazil. Moreover, by estimating a structural vector autoregressive (SVAR) model, I have empirically investigated the macroeconomic effects of unconventional monetary policies. Empirical findings of this study suggest that, unconventional monetary policies have lead a temporary increase in GDP and CPI for United States and United Kingdom while its effects are slightly significant for Japan and diametrically insignificant for Brazil.