The first six Danish kings named Frederick were also kings of Norway. The most important were:

(1609–1670), ruled 1648–70. He was the son of Christian IV. Renewed warfare with Sweden (1657–60) ended with the loss by Denmark of all territory on the Swedish mainland. At the end of the war, the king with the help of the middle class (to which he had granted political favors during the war) overthrew the powerful Danish nobility. Also, the monarchy, previously elective, was made hereditary.

(1768–1839), ruled 1808–39. Frederick became regent in 1784 because of the insanity of Christian VII, his father. Under his rule, serfdom was abolished and other reforms were made. Frederick reluctantly involved Denmark in the Napoleonic Wars (1800–14); the result was the loss of Norway and financial ruin for Denmark. In the latter part of his reign Frederick worked to rebuild his country.

(1808–1863), son of Christian VIII, came to the throne in 1848 Influenced by the Revolution of 1848 (a liberal movement that swept Europe), he renounced absolute rule, and in 1849 a constitutional monarchy was established. During his reign, the first Prusso-Danish war over Schleswig-Holstein was fought (1848–50), with Denmark victorious.

(1843–1912) succeeded his father, Christian IX, in 1906. Upon becoming king, he proposed a system of home rule for Iceland. His second son became King Haakon VII of Norway. Frederick was succeeded by his eldest son, Christian X.

(1899–1972), son of Christian X, became king in 1947. He had served as regent several times during the latter part of his father's reign. He was an admiral in the Danish navy and was also an accomplished musician. Frederick married Princess Ingrid of Sweden in 1935. He was succeeded by their daughter Margrethe.