A YouTube account is only necessary to watch adult-rated content on YouTube; all other videos can be viewed without an account. However, users who register for YouTube accounts have access to many features that non-registered visitors do not. Those with existing Google accounts can use their accounts to sign in to YouTube instead of creating new accounts.
With a YouTube account or Google account, visitors can interact with other YouTube account holders and leave comments on videos. They can also use YouTube's like feature to give a "thumbs up" or "thumbs down" rating to videos to express whether they like the video or not. Other features accessible with an account include the ability to upload videos, create a channel and create playlists to watch later.