1) It will depend on what the to-be-included file contains, e.g. if it contains a vital variable that the script depends on, it will most likely fail to execute. But this depends entirely on the situation. 2) The code you include can be two things: 1 - a text file, that will appear on the place where you place the include code. 2- a php file wich needs to be executed, in opposition to a text file, a php file to-be-included does need to have the <? or <?php starting and ?> ending-tags in the file. 3) I don't really know the difference between the include() and require() functions either, I preffer include(), but it could be that require() has a higher level of dependance or something. Check the php.net documentation for that Edit: