The history of Italy as a 'province' of Rome is covered extensively in the Roman history section of this site. Thus, this page provides a very brief overview on Roman administration of Italia.
Italy, being the home of the city of Rome itself, was of course the first step towards establishing Rome as a Mediterranean power. Long after the Etruscan Kings had been thrown out of Rome and the Republic was established, the Roman people would inevitable come into conflict with their immediate neighbors. The conquest, and assimilation of the Italian tribes, was the vital building block that would eventually establish Roman hegemony throughout the western world.
It was home to a diverse number of tribes and ethnicities. Near Rome, the region was dominated first by the Etruscan civilization, which contributed a great deal to Roman culture as a whole, and then by the Latin people. Rome first subdued and controlled the region of Latium as early as the 5th and 4th centuries BC, and would become embroiled with outer neighbors, the Samnites and even the Greek city states of southern Italy in turn. In the far north, in what was called Cisalpine Gaul (or Gaul this side of the Alps), the Romans would also face the challenge of incorporating Celtic tribes into the Roman fold. Though, this part of what we now include in modern Italy wasn't considered a part of Roman Italy until the reign of Augustus.
The Italian tribes weren't completely incorporated as Roman citizens until the late era of the Fall of the Republic and the Imperial regime. Prior to citizenship, the class status of the tribes was determined on a tribe by tribe, or according to region and town basis. Though some tribes were allowed 'Latin rights' giving them limited privileges under Roman law, there was a wide discrepancy in social status. These discrepancies, coupled with the forced conscription of Roman 'allies' to fight in their wars without voting rights in Rome, led to a great deal of social disorder throughout the Republic. As more tribes were incorporated into the Roman system, the battle for citizenship, limited rights and social equality was a recurring theme that helped tear down the fabric of the Republican government.
One of the great reasons for the emergence of Rome as an ancient power was the vast wealth of Italy and surrounding environs such as Sicily. The huge and fertile region of the Po River was a vital and productive area for early Roman farms. The Apennine Mountains dominated much of central and southern Italy, and the area was heavily forested. This, of course, provided easily accessible timber and quarries to allow the spread of Roman civilization without the need for vast imports, at least early on. Grain products such as corn, wheat and barley were grown in abundance, while the olive and grape became a staple part of Roman culture, remaining so until the present day.
The 91,000 square miles of Italy fell under the direct supervision of the Senate in the Republic and remained so, though with Imperial authority, during the Empire. Various magistrates took part in administering the government, including the local Praetors, who held authority typically for maintaining law, order and justice throughout the region. Various curators saw to such tasks as the construction of roads, aqueducts and public works, but these duties were as much a part of the Roman city administration as they were a part of Italy in its entirety. Prior to the complete consolidation of Italy, Legions were obviously present in order to not only defend Rome but to spread its influence. Once Roman authority was established in neighboring provinces such as Gaul, Hispania and on the Greek Peninsula, standing armies were not garrisoned in Italy, unless forced to by necessity. Aside from Legions being levied among the residents, and trained locally, a permanent legionary presence wasn't present in Italy for nearly 500 years. Aside from the Emperor's personal legions, the Praetorians, the regular army was only stationed in Italy for brief periods during civil wars, defense against invasions and when the empire was in shambles in the 5th century AD.
With the ascension of Augustus after the civil wars of the 1st century BC, Italy was reorganized into several districts for easier administration. Through these measures, he essentially established the word 'Italia' as it relates to the whole of the country, rather than individual regions within it. He established 11 regions that made up the whole of Italia comprising 1. Latium (including Rome), 2. Apulia and Calabria, 3. Lucania and Bruttiuin, 4. Samnium, 5. Picenum, 6. Umbria, 7. Etruria, 8. Cisalpine Gaul, 9. Liguria, 10. Venetia and 11. Transalpine Gaul. This organization of Italy remained in effect until the 4th century provincial reforms of Constantine into the Diocese.