set UTF-8 for a file (HTML)

[ken]

I'm editing an HTML file (in emacs, of course) and want to preserve the 
utf-8 encoding when the file is opened in subsequent sessions.  I know I 
can put a line at the top of the file which will set a variable in emacs 
whenever the file is opened.  So what should this line say to specify 
that the file is encoded in utf-8?
Thanks.

--
The significant problems we face cannot be solved at the
same level of thinking we were at when we created them.
        -- Albert Einstein