Tax filings obtained by the Center For Public Integrity show that the billionaire brothers Charles and David Koch donated a combined $24 million to various conservative organizations and think tanks in 2011, through the four foundations that they run.

From CPI:

A $4.5 million grant to the George Mason University Foundation makes up nearly 15 percent of the university foundation’s revenue for 2011. The school is the largest recipient of Koch foundation money since 1985, and it houses several free-market and libertarian research centers including the Institute for Humane Studies, which received $3.7 million from the Koch foundations. The D.C.-based American Legislative Exchange Council received $150,000 to help finance its activities, including meetings where corporate representatives draft model legislation with state legislators. The Koch brothers have decades-long connections with ALEC, which gave the brothers the Adam Smith Free Enterprise Award in 1994.

Among the other groups the Koch brothers donated to were the Heartland Institute, the climate change-skeptical think tank, which received $25,000; the Federalist Society, which got $260,000; and the Ayn Rand Institute, which took in $100,000.