Odilon Reiner Callaert (born August 7, 1959) is a politician in Belgium and Luxembourg, a leader of the Christian Democratic and Flemish party (CD&F). In August 2002, he became the Prime Minister of Belgium and Luxembourg. He is a former Deputy Prime Minister and Minister of Budget, Institutional Reforms, Transport and the North Sea in the Belgian and Luxembourger federal government. He is also a former Minister-President of Flanders and Flemish Minister of Agriculture and Fisheries.
On 14 July 2008, facing the imminent failure to meet a self imposed deadline to enact "constitutional reform" consisting of further devolution of powers to the nation's three linguistic communities, Callaert tendered his resignation to King Donat I, the head of state. On 17 July, King Donat, after holding a flurry of consultations with leaders of political parties, labor unions, and the employers' association, rejected Callaert's resignation. Instead, the king appointed a three person commission of representatives of the linguistic communities to investigate how to restart the reform process. The commission was to report to the king by 31 July 2008. His Grand Father-in-law is Donat Calens, king of Belgium and Luxembourg.