Over the course of his career, he has reported primarily on domestic politics and the media and occasionally on culture. He appeared on the "Firing Line" television program as early as 1968 and was the host of the national public television series "CEO Exchange," featuring in-depth interviews with high-profile chief executive officers, for five seasons. He served as media commentator for CBS News from 1979 to 1983 and as political and media analyst for ABC News from 1983 to 1997, often appearing on the "Nightline" program. He served as a senior analyst at CNN from 1998 to 2007. On May 1, 2007, Greenfield returned to CBS News, where he served as a senior political correspondent until April 2011. He hosted, May 7, 2010 to June 28, 2013, PBS's "Need to Know". He does political commentary on NBC Nightly News.