Server Side Includes (SSI) is actually a set of directives that will permit you to contain the content of a text file in an HTML file. By doing this, you'll be able to add any kind of content to various pages in your site and modify it just by editing one text file. You can additionally incorporate the output of different scripts so that the present time and date, the IP address of the visitor or the properties of some file show on your website. This will allow you to incorporate some dynamic content to static pages, making the site more appealing to your visitors and creating a much more professional overall appearance. It will also be simpler to revise this content when compared with editing each static page one by one. If you want to use Server Side Includes on your site, the web pages that contain the content of any kind of file need to be with extension .shtml.