The Passport Index has just released its annual Global Passport Power Rank for 2018. Countries are ranked by how many other countries a passport holder can get into without a visa, or with only a visa upon arrival.
The ranking has a rival, however, and the two disagree on specific criteria, resulting in variance in the most powerful passports. The Henley Passport Index ranks Japan as the most powerful passport. In the Henley ranking, there is no score difference between requiring no visa and requiring a visa upon entry.
There is also frequent fluctuation in the results, as diplomatic relations between countries are constantly shifting.