Japan, although currently the world's third largest economy behind the United States and China, has faced many challenges in recent years. The period from 1990 to 2010, in Japan, is even often referred to as "the lost 20 years". This name, which does not evoke anything positive, refers to a period when Japan faced weak economic growth and persistent deflation despite relatively low interest rates. During this period, the Bank of Japan has made many attempts to deal with this long crisis. It was a pioneer in developing and implementing so-called unconventional monetary policies. These monetary policies, such as quantitative easing, are now used by the majority of the world's major central banks, such as the FED. In this paper, I analyse and try to understand how the Bank of Japan made its monetary policy decisions during the last 20 years. I use social learning theory, to which I make several modifications, as a tool to analyse the policymaking of the Bank of Japan during the lost 20 years. Thanks to that, the paper also provides a reflection on the theory of social learning, described by Hall in his article of 1993. This reflection on social learning has made it possible to make social learning more general, which makes it possible to use this theory in a multitude of other cases. The other major contribution of this thesis is that it offers an innovative analysis of the policymaking of the Bank of Japan during the lost 20 years. In addition to this, I provide several other insights into the Bank's policymaking in the literature review.