Johann II (German: Johann Maria Franz Placidus; 5 October 1840 – 11 February 1929), a.k.a. Johann II der Gute or Johann II the Good, was the Prince of Liechtenstein between 1858 and 1929. His reign of 70 years and 90 days is the second-longest in European royal history after that of Louis XIV of France who, however, was crowned at age 5.

Johann II was the elder son of Aloys II, Prince of Liechtenstein and Countess Franziska Kinsky of Wchinitz and Tettau. He ascended to the throne shortly after his 18th birthday, and as such his reign is the longest precisely documented tenure of any monarch since antiquity in which a regent was never employed.

In 1862, Johann II issued Liechtenstein's first constitution. Later, after Liechtenstein left the German confederation in 1866 and after World War I, Johann II granted a new constitution in 1921. It granted considerable political rights to common Liechtensteiners, the latter making the principality a constitutional monarchy. This constitution survives today but with revisions, most notably in 2003.

Liechtenstein left the German Confederation in 1866. Not long after, the army of Liechtenstein was abolished as it was regarded as an unnecessary expense.

Johann II somewhat cooled relations with Liechtenstein's traditional ally, Austria-Hungary and its successor states, to forge closer relations with Switzerland, particularly after World War I. Liechtenstein was neutral during World War I, but the war broke Liechtenstein's alliance with Austria-Hungary and led it to go into a customs union with Switzerland. Late in Johann's reign, in 1924, the Swiss franc became Liechtenstein's official currency.

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