Karen Mills is leaving the U.S. Small Business Administration (SBA) after nearly four years of leading the agency, the Washington Business Journal reported. Mills announced her decision Monday in a letter to SBA employees, which thanked them for their role "to help America's entrepreneurs and small business owners during this critical juncture in our nation's history." Mills, who has an M.B.A. from Harvard Business School, ran her own private equity firm before joining the SBA. She said the agency's loan programs played a major role in unfreezing credit to small businesses. In the past four years, the SBA has backed more than $106 billion in loans to 193,000 small businesses, including two years of record lending thanks to those now-expired stimulus incentives.