If you use server side includes (SSI), then there are:
<!-- #include file="path/to/includedfile.inc" -->
<!-- #include virtual="/path/to/includedfile.inc" -->
SSI will only work in asp.NET, asp, pup, and .shtm and .shtml pages. SSI
will NOT work in any page that requires FrontPage extensions at run time.
..htm pages will work with SSI only if the server is set up to allow it.
In the above path/to/ represents the relative path from the page to the
included page. Some servers will not allow parent paths ( ..\ etc)
/path/to/ represents the path to the included page from the website root
folder.
The only other way to include a page is to use an iFrame.