Inheritance

Often two classes will have similar methods
For example, consider Person
It supports name, age, spouse methods
An Employee is a special kind of person
It supports all the same methods, but also department and boss

        package Person;         package Employee;
        sub new    { ... }      (probably identical)
        sub name   { ... }      (identical)
        sub age    { ... }      (identical)
        sub spouse { ... }      (identical)
                                sub boss       { ... }
                                sub department { ... }

Reimplementing identical methods in the Employee class is a waste