Engineering design company Aecom Technology Corp. says it is buying URS Corp. for $4 billion in cash and stock, or about $56.31 per URS share.
The price is 8 percent above URS's closing stock price Friday.
The California-based companies said Sunday the combination was necessary to building an integrated infrastructure services company that can operate globally and provide services including design, financing, construction and operation of buildings.
The companies had worked together on projects such as the Barclays Center in Brooklyn and the World Trade Center in New York.
The offer includes $33 per share in cash and 0.734 Aecom shares for every URS share.
URS CEO Martin Koffel said in a conference call the deal gives its shareholders "a ride on the future as well as a cash takeout."