Difference between "include" and "require" in php

require will throw a PHP Fatal Error if the file cannot be loaded. (Execution stops)

include produces a Warning if the file cannot be loaded. (Execution continues)

Here is a nice illustration of include and require difference:

From: Difference require vs. include php (by Robert; Nov 2012)

You find the differences explained in the detailed PHP manual on the page of require:

require is identical to include except upon failure it will also produce a fatal E_COMPILE_ERROR level error. In other words, it will halt the script whereas include only emits a warning (E_WARNING) which allows the script to continue.

See @efritz's answer for an example