Using the extends keyword to define a subclass
<?php class Cat { var $age; function Cat($new_age){ $this->age = $new_age; } function Birthday( ){ $this->age++; } } class MyCat extends Cat { function MyCat( ) { } function sleep( ) { echo("Zzzzzz.<br />"); } } $fluffy=new MyCat( ); $fluffy->Birthday( ); $fluffy->sleep( ); echo "Age is $fluffy->age <br />"; ?>