Following the Fukushima nuclear disaster of 2011, the Japanese Cabinet, the Japanese Diet, a private-sector group as well as the operator of the Fukushima Daiichi nuclear facility, TEPCO, each set up an investigation commission to examine the causes of the accident, scrutinize the crisis response and make recommendations for future policies. This article provides some background on the four commissions and then examines and assesses the contents of the reports. Four key conclusions emerge from the analysis. Firstly, the establishment of the commissions was accompanied by immense mistrust, as each of the initiators suspected bias in the other inquiries. Secondly, the comparison demonstrates that while biases can be detected to some extent, the four reports overall agree in their identification of fundamental issues and crucial problems. Thirdly, the article maintains that the four reports used in combination convey a more complete picture than any single one of them. A comparison of the reports highlights diverging interpretations and differing degrees of criticism, while exposing open questions and unresolved issues. Finally, the article argues that the four investigation reports can serve as important reference points, enabling critical assessments of reforms currently undertaken in Japan's nuclear power administration and crisis management system.