US President Barack Obama and First Lady Michelle Obamahas arrived in India for a three-day visit amid an unprecedented security operation.
Thousands of security personnel have been deployed in Delhi along with some 15,000 cameras.
Prime Minister Narendra Modi stressed the importance of the visit by breaking protocol to receive Mr Obama personally at Delhi airport.
Their talks will primarily focus on trade, but also take in security, nuclear power and climate change.
Mr Obama will also be the guest of honour at Monday’s Republic Day celebrations.
After his arrival, the US president travelled to the presidential palace, Rashtrapati Bhavan, for an official welcoming ceremony with his Indian counterpart Pranab Mukherjee.
Mr Obama said: “This is a great honour, we are grateful for this extraordinary hospitality.”
President Obama, who is the chief guest of this year’s Republic Day parade, will be the first U.S. president to attend the Republic Day celebrations.Obama, who visited India in 2010, will also be the first US president to visit the country twice while in office.