When Stefani Germanotta burst onto the scene a few years ago, we're willing to bet that the singer/songwriter from the Lower East Side couldn't imagine just how successful she would become. Or, maybe she did? In honor of Lady Gaga's 26th birthday, we gathered 15 irresistible Gaga photos captured by Mario Testino, Annie Leibovitz, Terry Richardson, and cast of other world class photographers. The reigning Queen of Pop has appeared on numerous magazine covers and in pages of Vogue, Rolling Stone, and Harper's Bazzar just to name a few. Since we didn't get her a cake, celebrate by counting down the 15 most irresistible Lady Gaga photo shoots.

Check out The 15 Most Irresistible Lady Gaga Photo Shoots gallery.