In their own words:
Media Matters for America is a Web-based, not-for-profit, 501(c)(3) progressive research and information center dedicated to comprehensively monitoring, analyzing, and correcting conservative misinformation in the U.S. media.
Launched in May 2004, Media Matters for America put in place, for the first time, the means to systematically monitor a cross section of print, broadcast, cable, radio, and Internet media outlets for conservative misinformation — news or commentary that is not accurate, reliable, or credible and that forwards the conservative agenda — every day, in real time.
Using the website www.mediamatters.org as the principal vehicle for disseminating research and information, Media Matters posts rapid-response items as well as longer research and analytic reports documenting conservative misinformation throughout the media. Additionally, Media Matters works daily to notify activists, journalists, pundits, and the general public about instances of misinformation, providing them with the resources to rebut false claims and to take direct action against offending media institutions.