Jens Otto Krag (Danish pronunciation: [ˈjens ˈʌtsʰo ˈkʰʁɑˀw]; 15 September 1914 – 22 June 1978) was a Danish politician, who served as the prime minister of Denmark from 1962 to 1968 and again from 1971 to 1972, and as leader of the Social Democrats from 1962 to 1972. He was president of the Nordic Council in 1971.

Krag was born on 15 September 1914 in Randers, Jutland, into the impoverished family of a tobacconist. Krag attended the local gymnasium, and as a teenager, he joined the Social Democratic Youth of Denmark, the youth wing of the Social Democrats. In 1933, Krag began studying economics at the University of Copenhagen. During this period, he emerged as an active journalist and teacher in the labour movement, and became acquainted with the leadership of the Social Democrats and the trade unions.

Following the Nazi invasion of Denmark, Krag received his degree in 1940. During the Nazi occupation, Krag worked as a civil servant in a Danish government agency and became a leading economic advisor to the labour movement, as well as a protégé of prominent social democrat and future prime minister Hans Hedtoft.

In 1944, Krag began his political career as the secretary of a program committee set up by the Social Democratic Party, as it prepared itself for politics in the post-war period. Under his leadership, the committee developed the new party program "Denmark of the Future" (Fremtidens Danmark), which presented proposals for nationalisation and notions of Keynesian economics and economic democracy. Despite the party's poor performance in the first post-war election in 1945, Krag and new party program of the Social Democrats achieved notoriety in Danish politics under Vilheim Buhl's cabinet.

Krag was elected to Parliament (Folketing) in 1947 and was appointed Minister of Commerce. He supported the strengthening of the Danish military and Danish membership of NATO in 1949.

In 1950, Krag resigned from Parliament partially due to a conflict with Vilhelm Buhl and H. C. Hansen and, in order to become more fluent in the English language and see more of the world, requested a position at the Danish embassy in the United States. He received the position, and was in America until 1953 when he was re-elected to parliament and became a minister without portfolio. He was minister of the new department of foreign economic affairs from 1953 until 1958 and Foreign Minister from 1958 until 1962.

In September 1962 he succeeded Viggo Kampmann as prime minister and leader of the Danish Social Democratic Party. He was prime minister until February 1968 when the Social Democrats lost power. He became prime minister again in 1971 when his party returned to power. Less than a year into his first term as prime minister, the opposition held a referendum which rejected a set of land laws already passed by Krag's government.

During his second term as prime minister, Krag campaigned particularly for European cooperation and unity. He sponsored a referendum for Denmark to join the European Economic Community. In 1972 the referendum passed, but the nation was divided over the issue, and Krag resigned, claiming that he had become tired of politics. His last role in public life was as the European Common Market representative to the United States from 1974 until 1975.