The investigation follows a number of complaints alleging unfair commercial practices by the tech giants.
"The proceedings relate to alleged unfair commercial practices and the possible presence of unfair clauses in the contractual terms and conditions," Italy's AGCM said a statement on Monday.
The authority has launched six investigations in total, including over alleged violations of Italy’s Consumer Rights Directive.
All three companies are being probed over complaints of unfair practices by failing to adequately indicate to users when their data is being collected for commercial purposes.
Dropbox is also being investigated to provide clear information on the terms and procedures for withdrawing from the contract. The AGCM is also examining Dropbox's terms on access to out-of-court dispute settlement mechanisms.
Other lines of inquiry are also looking at concerns of unfairness include the rights for providers to suspend service, liability exemptions in the event of loss of documents stored in the cloud space, and the prevalence of the English version of the contract text over the Italian version.
Euronews has contacted Apple, Dropbox, and Google for statements in response to the investigation.
In recent years the European Commission has pushed for co-ordinated action against tech companies over their terms and conditions.
In 2018, the AGCM fined Facebook €10 million for misleading users over the company's data practices.
The authority also found against Apple in another case two years ago, over the company's intentional slowing down of iPhones with older batteries. Apple has unsuccessfully appealed against the decision.