On December 3, 2007 the Diamondbacks traded Carlos Quentin to the Chicago White Sox for first base prospect Chris Carter.

On December 14, in a blockbuster trade, the Diamondbacks acquired starting RHP Dan Haren from the Oakland Athletics for six players: LHP Brett Anderson, LHP Dana Eveland and LHP Greg Smith; the above-mentioned just-acquired infielder Chris Carter; and outfielders Aaron Cunningham and Carlos Gonzalez. The team also traded relief pitcher Jose Valverde, who led the major leagues in saves in 2007 with 47, to the Houston Astros for reliever Chad Qualls, RHP Juan Gutiérrez and IF/OF Chris Burke. (Valverde was expected to immediately become the Astros' closer.)

Haren was expected to immediately join the Diamondbacks starting rotation which will include Webb and hopefully Randy Johnson if he rehabilitates successfully from his season-ending back injuries (Johnson was acquired from the Yankees in January 2007 and had a strong start to the 2007 season before back problems forced him out in August).

Haren was 15-9 with a 3.07 ERA for Oakland in 2007. This move was expected to make the D-backs favored to win the NL West in 2008 provided the offensive production is good.