The Union was a heterogenous centre-left political and electoral alliance of political parties in Italy. The Union was the direct heir of The Olive Tree coalition which represented the centre-left in the 1996 and 2001 general elections. However, The Union also included parties of the radical left, which were not affiliated with The Olive Tree. The Union was led by Romano Prodi, Prime Minister of Italy from May 2006 to May 2008, and former President of the European Commission. Collapsing in the wake of the 2008 Italian political crisis, the alliance was succeeded by the current-day centre-left coalition.

The Olive Tree was a denomination used for several successive centre-left political and electoral alliances of Italian political parties from 1995 to 2007.