CNN (Cable News Network), an American basic cable and satellite television channel, has been the subject of multiple controversies. This article recounts controversies and allegations relating to both the domestic version of CNN, and its sister channels CNN International and CNN-News18.

CNN has often been the subject of allegations of party bias. The New York Times has described its development of a partisan lean during the tenure of Jeff Zucker. In research conducted by the Shorenstein Center on Media, Politics and Public Policy at Harvard University and the Project for Excellence in Journalism, the authors found disparate treatment by CNN of Democratic and Republican candidates during the earliest five months of the Democratic and Republican primaries in 2007: "The CNN programming studied tended to cast a negative light on Republican candidates—by a margin of three-to-one. Four-in-ten stories (41%) were clearly negative while just 14% were positive and 46% were neutral. The network provided negative coverage of all three main candidates with McCain fairing the worst (63% negative) and Romney fairing a little better than the others only because a majority of his coverage was neutral. It's not that Democrats, other than Obama, fared well on CNN either. Nearly half of the Illinois Senator's stories were positive (46%), vs. just 8% that were negative. But both Clinton and Edwards ended up with more negative than positive coverage overall. So while coverage for Democrats overall was a bit more positive than negative, that was almost all due to extremely favorable coverage for Obama." In a New York Observer column entitled "Clinton News Network", political journalist Steve Kornacki criticized CNN's handling of the November 15, 2007, Democratic presidential debate, calling it biased towards Hillary Clinton.

In September 2009, a Pew Research Center Poll showed that Democrats were much more likely than Republicans to rate the network favorably, while Republicans were much more likely than Democrats to see CNN unfavorably. A 2019 Pew Research survey showed that among Americans who named CNN as their main source for political and election news, 79% identify as Democrats whereas 17% identify as Republicans. Among major broadcast news networks, the CNN audience displays higher levels of partisanship than ABC, CBS and NBC, but lower than Fox News and MSNBC.

In 2011, Chief Middle East correspondent Octavia Nasr was fired after a tweet saying she was "Sad to hear of the passing of Sayed Mohammad Hussein Fadlallah... One of Hezbollah's giants I respect[ed] a lot." Parisa Khosravi, senior vice president of CNN International, said she spoke with Nasr, and "we have decided that she will be leaving the company". Her reason for her removal was given as "As you know, her tweet over the weekend created a wide reaction. As she has stated in her blog on CNN.com, she fully accepts that she should not have made such a simplistic comment without any context whatsoever. However, at this point, we believe that her credibility in her position as senior editor for Middle Eastern affairs has been compromised going forward."

On April 3, 2016, hundreds of supporters of Bernie Sanders protested outside of CNN's Los Angeles bureau on Sunset Boulevard. Sanders supporters were protesting CNN's coverage of the 2016 United States presidential elections, specifically in regard to the lack of airtime Sanders had received. Known as Occupy CNN, protesters claimed that major media networks have intentionally blacked out Sanders' presidential campaign in favor of giving much more airtime to candidates such as Hillary Clinton.

In October 2016, WikiLeaks published emails from John Podesta which showed CNN contributor Donna Brazile passing the questions for a CNN-sponsored debate to the Clinton campaign. In the email, Brazile discussed her concern about Clinton's ability to field a question regarding the death penalty. The following day Clinton would receive the question about the death penalty, verbatim, from an audience member at the CNN-hosted Town Hall event. According to a CNNMoney investigation, debate moderator and CNN contributor Roland Martin (now with TV One) "did not deny sharing information with Brazile". CNN severed ties with Brazile on October 14, 2016. Brazile then resigned from CNN in October 2016 due to the revelations.

During live coverage of the 2016 elections, CNN anchor Chris Cuomo said that downloading the hacked and stolen Podesta emails from the WikiLeaks website was a violation of law and that only the media could legally do so. The statement was proven to be false and drew criticism to the network.

Following the 2020 Democratic Party presidential primaries debate moderated by CNN and the Des Moines Register on January 14, 2020, CNN was accused by various media pundits of bias towards centrist candidates. The debate moderation by CNN was described by Rolling Stone's Matt Taibbi as "villainous and shameful", and Zach Carter at The Huffington Post said the debate moderation was "awful", with Carter writing, "Again and again, CNN anchors substituted centrist talking points for questions―and then followed up predictable responses with further centrist talking points, rarely illuminating any substantive disagreements between the candidates or problems with their policy positions". Jeet Heer, the national affairs correspondent at The Nation said "the big loser of the night was the network that hosted the event. CNN was so consistently aligned against Bernie Sanders that it compromised its claim to journalistic neutrality."