From Dolce & Gabbana's Swide blogazine:

Madonna has joined forces with Italian designers Dolce & Gabbana to showcase their spring/summer 2010 collection in the brand's forthcoming ad campaign. The campaign will be shot today in New York by photographer Steven Klein.
Madonna first met the designers Stefano Gabbana and Domenico Dolce back in the early nineties and have retained a strong bond and mutual respect ever since. After first meeting the global superstar whilst she was on the set of Dick Tracy in New York, the designers went onto design her costumes for the now iconic, The Girlie Show tour in 1993.
As Dolce & Gabbana's spring/summer 2010 collection returned to the Italian roots of the brand, evoking its strong heritage and revisiting iconic pieces such as the corset (the designer's finale was composed solely of corsets) it seemed only fitting that Madonna, who embodies both the strong sensuality of the brand and who shares an Italian heritage with the designers should be the one to showcase the Sicilian inspired collection.
On Madonna appearing in their forthcoming campaign, Domenico Dolce and Stefano Gabbana said:
"To have Madonna in our campaign is a dream come true".
Dolce & Gabbana's spring/summer 2010 campaign is being shot on November 6th in New York by fashion photographer Steven Klein.

Sources: Dolce & Gabbana, MadonnaTribe