Which earlier Supreme Court decisions did Citizens United v. Federal Election Commission overturn?

In the 2010 ruling of Citizens United v. Federal Election Commission, the U.S. Supreme Court overturned two of its previous decisions, either in whole or in part:

• Austin v. Michigan Chamber of Commerce (1990): The Court overruled this decision, which had previously held that the government could prohibit corporations from using general treasury funds for independent political expenditures to prevent the "distortion" of the political process.12
• McConnell v. Federal Election Commission (2003): The Court overruled the portion of this decision that had affirmed the validity of Section 203 of the Bipartisan Campaign Reform Act (BCRA), which restricted corporate and union electioneering communications.12

By overturning these precedents, the Court held that the government's prohibition on corporate and union independent expenditures violated the First Amendment’s guarantee of freedom of speech.1