YouTube is an American online video-sharing platform headquartered in San Bruno, California, founded by three former PayPal employees—Chad Hurley, Steve Chen, and Jawed Karim—in February 2005. Google bought the site in November 2006 for US$1.65 billion, since which it operates as one of Google's subsidiaries.

YouTube allows users to upload videos, view them, rate them with likes and dislikes, share them, add videos to playlists, report, make comments on videos, and subscribe to other users. The slogan "Broadcast Yourself" used for several years and the reference to user profiles as "Channels" signifies the premise upon which the platform is based, of allowing anyone to operate a personal broadcasting station in resemblance to television with the extension of video on demand.

As such, the platform offers a wide variety of user-generated and corporate media videos. Available content includes video clips, TV show clips, music videos, short and documentary films, audio recordings, movie trailers, live streams, and other content such as video blogging, short original videos, and educational videos.

As of February 2017^[update], there were more than 400 hours of content uploaded to YouTube each minute, and one billion hours of content being watched on YouTube every day. As of October 2020^[update], YouTube is the second-most popular website in the world, behind Google, according to Alexa Internet. As of May 2019^[update], more than 500 hours of video content are uploaded to YouTube every minute. Based on reported quarterly advertising revenue, YouTube is estimated to have US$15 billion in annual revenues.

YouTube has faced criticism over aspects of its operations, including its handling of copyrighted content contained within uploaded videos, its recommendation algorithms perpetuating videos that promote conspiracy theories and falsehoods, hosting videos ostensibly targeting children but containing violent or sexually suggestive content involving popular characters, videos of minors attracting pedophilic activities in their comment sections, and fluctuating policies on the types of content that is eligible to be monetized with advertising.

YouTube was founded by Chad Hurley, Steve Chen, and Jawed Karim, when they worked for PayPal. Prior to working for PayPal, Hurley studied design at the Indiana University of Pennsylvania; Chen and Karim studied computer science together at the University of Illinois at Urbana–Champaign. YouTube's initial headquarters was above a pizzeria and Japanese restaurant in San Mateo, California.

The domain name "YouTube.com" was activated on February 14, 2005, with an open beta on April 23, 2005, with the slogan "Tune In, Hook Up" ─ the original idea of Chad Hurley, Steve Chen, and Jawed Karim. The concept was an online dating service that ultimately failed but had an exceptional video and uploading platform. After the infamous Justin Timberlake and Janet Jackson Halftime show incident, they found it difficult to find any videos of it on the internet. After noticing that a video sharing platform did not exist, they dropped the dating aspect of the site. The idea of the new company was for non-computer experts to be able to use a simple interface that allowed the user to publish, upload and view streaming videos through standard web browsers and modern internet speeds. Ultimately, creating an easy to use video streaming platform that wouldn't stress out the new internet users of the mid-2000s. The first YouTube video, titled Me at the zoo, was uploaded on April 23, 2005, and shows co-founder Jawed Karim at the San Diego Zoo and currently has over 355 million views and 17 million likes. Hurley was behind the look of the website, creating the logo. Chen made sure the page actually worked and that there would be no issues with the uploading and playback process. Karim was a programmer and helped in making sure the initial website was put together properly and helped in both design and programming.

As of June 2005, YouTube's slogan was "Your Digital Video Repository".