Public administration has historically been difficult to define. Nonetheless, we all have a general sense of what it is, though we may disagree about how it should be carried out. In part, this is because public administration involves a vast amount of activity. Public sector jobs range from providing homeland security, to the exploration of outer space, to sweeping the streets. Some public administrators are highly educated professionals who may be at the forefront of their fields of special expertise (like NASA engineers and rocket scientists); others possess few skills that differentiate them from ordinary workers. Some public administrators make policies that have a nationwide impact and may benefit millions of people; others have virtually no responsibility for policy making and simply carry out mundane but necessary clerical tasks. Public administrators are doctors, lawyers, scientists, engineers, accountants, budgeters, policy analysts, personnel officers, managers, baggage screeners, clerks, keyboarders, manual laborers, and individuals engaged in a host of other occupations and functions. But knowing what public administrators do does not resolve the problem of defining what public administration is.