Two Italian marines are to go on trial in India accused of murdering two fishermen last year.
Italy's surprise decision to return the marines followed intense negotiations.
In the negotiations Rome secured a vow from New Delhi that the two would not face the death penalty if convicted.
The marines were part of a military security team protecting a tanker from piracy in last February.
They are accused of shooting the fishermen off the southern Indian state of Kerala.
The marines said they fired warning shots at a fishing boat believing it to be a pirate vessel.
Salvatore Girone and Massimiliano Latorre flew back to India today on an Italian air force plane accompanied by Italian Deputy Foreign Minister Staffan de Mistura.
Italian President Giorgio Napolitano told the pair that he "appreciated the sense of responsibility demonstrated in their acceptance of the government's decision".
India and Italy have been embroiled in a sharply escalating diplomatic row over the marines.
The marines had been allowed to leave India to vote in the Italian elections in February on condition they returned by today.
However, Rome informed New Delhi on 11 March that they would not be returning to stand trial.
The Indian government demanded Italy return the sailors or face a possible rupture in ties.
India's chief justice went so far as to bar Italy's ambassador from leaving the country.
The chief justice's ruling sent ripples of concern through the diplomatic community in New Delhi.
The European Union warned India it would be violating international law if it tried to enforce the decision.
Details of the negotiations have not been disclosed.
Sources said India and Italy had an agreement under which sentenced prisoners could serve jail time in their home countries.
Indian Foreign Minister Salman Khurshid said in parliament that India had assured Italy that the marines would not face the death penalty, which only applied in the "rarest of rare cases".
