Congresswoman Gabrielle Giffords, who was shot in the head last January during an attack on a gathering in Tuscon, Arizona, at which several of her constituents were killed, resigned her congressional seat Wednesday morning to focus on her recovery.

Rep. Debbie Wasserman spoke on Giffords' behalf in a tearful address to Congress. "I know, being able to be Gabby's voice today, knowing her as well as I do, that she wants her constituents to know... that it has been the greatest privilege of her professional life to represent them," she said, her voice breaking throughout.

In her letter of resignation to House Speaker John Boehner, dated January 25, she expressed grief for those who died in the Jan. 8, 2011, attack, explained her reasons for leaving and promised to return one day to public service. 

"From my first steps and first words after being shot to my current physical and speech therapy, I have given all of myself to being able to walk back onto the House floor this year to represent Arizona's 8th Congressional District," she wrote. "However, today I know that now is not the time. I have more work to do on my recovery before I can again serve in elected office."

This came after an emotional moment at Tuesday night's State of the Union address, at which Giffords was honored in Congress.