Usage Recommendation
Use it, but be aware that many browsers use underline to indicate a link.

<U> underlines the enclosed text.

My favorite book is <U>To Kill a Mockingbird</U>


My favorite book is To Kill a Mockingbird

It's generally best to avoid <U>. Most browsers default to using an underline to indicate a link, so a plain underline that isn't a link is confusing. If you want to designate the name of a book, try italics instead:

My favorite book is To Kill a Mockingbird

About the Author
Copyright 1997-2002 Idocs Inc. Content in this guide is offered freely to the public under the terms of the Open Content License and the Open Publication License. Contents may be redistributed or republished freely under these terms so long as credit to the original creator and contributors is maintained.