A congressional government is different from a parliamentary government as it does not have a Prime Minister. The congress may have a nominal head, but usually the powers of Head of State and Head of Government rest with a president who is not a member of the legislative branch. For this reason, the term congressional system is often used interchangeably with presidential system.
The other key difference is a congressional government rarely uses the principle of the vote of no confidence, and as a result tends to have very weak party discipline.
Nations with congressional governments are the United States, Mexico, Switzerland, and most nations in South America.
See also: republic