If you only have HTML on your server, or you need only HTML files, you can use frames.
or iframes like this (in your index.html file):
But, it is not recommended as it creates a kind of table. If you have PHP on your server, create a PHP file, and use
include("header.html");
If you have SSI (Server Side Includes) on your webserver, then have this:
Personally, I suggest you to use PHP method.
