YouTube

2005-present
The logo consists of a black "You" and a red rounded rectangle with the word "Tube" in it. It can also contain the "Broadcast Yourself" tagline underneath. It was originally scheduled to be released in 2003, but was delayed until 2005.

2005–2011 (official use), 2011-present (secondary)
As of 2011, this is now being used as a secondary logo.

2011–2013
This modification of the YouTube logo was introduced in July 2011 as a part of the Cosmic Panda experiment. It officially became the new logo a few months later. With the introduction of the entirely new layout on December 6, 2012, the slogan "Broadcast Yourself" was retired.

2013–present (as alternate logo)
This logo was introduced on August 29, 2013, particularly used on Facebook and Twitter accounts. Also used for app icons (e.g Windows Server 2012, Windows 8, and Nokia Windows Phones.)

2013–present (as main logo)
In December 19, 2013, the red tube was made slightly lighter in color.

Website History
This is a look at YouTube's website over the years.

Yoodles
Like Google with their Doodles, YouTube changes their default logo to a stylized one with relevance to a certain date on various days throughout the year. These special logos are sometimes called Yoodles.