Massive holding company Omnicom is set to acquire acquire IPG, itself a holdco of several major agencies, for $13.25 billion.

Omnicom has agreed a deal to acquire Interpublic to create the world’s biggest agency group, the two companies have formally announced to the US stock market. The two agency groups said their respective boards of directors had unanimously approved the all-stock transaction and hailed their “complementary” assets and cultures in a joint statement.