Indian officials have signed agreements to hand over the Delhi and Mumbai (Bombay) airports to private companies who will develop them.
New terminals are planned for Mumbai and Delhi airports
"The Operations, Maintenance and Development Agreements and the share holders agreements have been signed," India's aviation minister said.
In January, the government announced that the two airports will be leased to private companies.
The move was opposed by trade unions and airport employees.
The GMR group, a leading construction firm based in south India, won the contract to modernise Delhi airport along with its German partner Fraport.
Another leading construction company, GVK, won a similar contract for Mumbai airport with Airports Company of South Africa (ACSA).
The airports will now be run as joint ventures between the private companies and the government, which retains a 26% stake.
"The JV (joint venture) companies are in place and their boards are meeting today," Indian Aviation Minister Praful Patel is quoted as saying by the Press Trust of India.
Both GMR and GVK are expected to build new terminals and passenger facilities at the overstretched airports.
Delhi and Mumbai account for almost 65% of India's international traffic of 19m passengers a year.
But the move to hand over the airports two months ago led to a four-day protest by thousands of airport workers and Communist parties.
They said the move would lead to job cuts.
The strike was called off after the aviation minister assured them that their interests would be kept in mind.