The function names __construct, __destruct (see Constructors and Destructors), __call, __get, __set (see Overloading), __sleep, __wakeup, and __toString are magical in PHP classes. You cannot have functions with these names in any of your classes unless you want the magic functionality associated with them. PHP reserves all function names starting with __ as magical. It is recommended that you do not use function names with __ in PHP unless you want some documented magic functionality. serialize checks if your class has a function with the magic name __sleep. If so, that function is being run prior to any serialization. It can clean up the object and is supposed to return an array with the names of all variables of that object that should be serialized. The intended use of __sleep is to close any database connections that object may have, committing pending data or perform similar cleanup tasks. Also, the function is useful if you have very large objects which need not be saved completely. Conversely, unserialize checks for the presence of a function with the magic name __wakeup. If present, this function can reconstruct any resources that object may have. The intended use of __wakeup is to reestablish any database connections that may have been lost during serialization and perform other reinitialization tasks. The __toString method allows a class to decide how it will react when it is converted to a string. foo = $foo; } public function __toString() { return $this->foo; } } $class = new TestClass('Hello'); echo $class; ?> ]]> &example.outputs; It is worth noting that the __toString method will only be called when it is directly combined with echo or print. ]]>