How to set HTTP header to UTF-8 using PHP which is valid in W3C validator

I have several [PHP][1] pages echoing out various things into [HTML][2] pages with the following code. <meta http-equiv="Content-type" content="text/html; charset=utf-8" /> However, when I validate using the [W3C validator][3] it comes up with: > The character encoding specified in the HTTP header (iso-8859-1) is different from the value in the <meta> element (utf-8). I am quite new to PHP, and I was wondering if I could and should change the header for the PHP files to match the HTML files. [1]: http://en.wikipedia.org/wiki/PHP [2]: http://en.wikipedia.org/wiki/HTML [3]: https://en.wikipedia.org/wiki/W3C_Markup_Validation_Service