Incumbents

Kingdom of Prussia
- Monarch –
  - Frederick William III of Prussia (16 November 1797 – 7 June 1840)^[1]
  - Friedrich Wilhelm IV (7 June 1840–1861)
Kingdom of Bavaria
- Monarch – Ludwig I (1825–1848)
- Prime Minister – Karl von Abel (1837–1847)
Kingdom of Saxony
- Frederick Augustus (1836–1854)
Kingdom of Hanover– Ernest Augustus (1837–1851)^[2]
Kingdom of Württemberg – William (1816–1864)

Events

June 7 – On the death of Frederick William III of Prussia, he is succeeded on the throne of the Kingdom of Prussia (which he has ruled for more than 40 years) by his eldest son Frederick William IV.
July 15 – The Austrian Empire, the United Kingdom, the Kingdom of Prussia, and the Russian Empire sign the Convention of London with the Sublime Porte, ruler of the Ottoman Empire.
The Rhine crisis of 1840 was a diplomatic crisis between the Kingdom of France and the German Confederation.

January 23 – Ernst Abbe, German physicist (d. 1905)
February 22 – August Bebel, German politician (d. 1913)
March 8 – Eduard von Knorr, German admiral (d. 1920)
March 16 – Georg von der Gabelentz, German linguist and sinologist (d. 1893)^[3]
March 28 – Emin Pasha, German doctor, African administrator (d. 1892)
July 2 – Ludwig Rosenthal, German antiquarian bookseller (d. 1928)
August 4 – Richard von Krafft-Ebing, German sexologist (d. 1902)