This paper comprehensively reviews and assesses Japan’s climate change mitigation policies. Its objectives are threefold. First, it assesses the ambition level of the Warsaw Target in comparison with the Copenhagen Pledge and earlier 2020 mitigation targets. Second, it reviews the development of mitigation-related policies since 2009, when national discussions on post-2020 climate mitigation efforts intensified. Third, it assesses whether Japan can meet the Warsaw Target through existing policies by comparing the Warsaw Target with “business-as-usual” GHG emissions projections.