During his visit, Mattis is scheduled to hold meetings with Sitharaman, PM Modi, and National Security Advisor Ajit Doval.
The visit is expected to bolster India-US defense ties, especially as Washington is rooting for a greater role for India in Afghanistan.
Jim Mattis arrives in India for 2-day visit
Why is this visit significant?
This marks the first cabinet-level visit to India under the Trump presidency and Sitharaman's first major engagement with a foreign counterpart. This is also the first engagement of its kind after Trump urged India to play a greater role in Afghanistan in August 2017.
What are the discussions likely to focus on?
Mattis is expected to discuss maritime security, a joint concern for India and the US in the face of the Chinese navy's increased presence in the Indian Ocean Region.
An announcement on a joint naval exercise focusing on Humanitarian Assistance and Disaster Relief (HADR) is expected.
The discussions will also focus on how India can pitch in with respect to Trump's Afghanistan strategy.
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Mattis to discuss drone sale, joint defense development
US defense majors Lockheed Martin and Boeing have both offered to manufacture their F-16 and F/A-18 fighter jets, respectively, in India to meet Indian Air Force and navy requirements.
Mattis would likely make the case for both US firms while meeting his Indian counterpart.
However, Trump's protectionist agenda could dent Modi's 'Make in India' program for defense production.
What does India expect from the visit?
The US designated India a major defense partner last year. India hopes for further elevation of bilateral defense ties in order to get better access to US defense technology.
Sitharaman and Mattis are also expected to develop the sort of equation that India's former defense minister Manohar Parikkar shared with former US defense secretary Ash Carter, which had helped push bilateral defense ties forward.
26 Sep 2017
Sitharaman to Mattis: India won't deploy troops in Afghanistan
Defense Minister Nirmala Sitharaman has ruled out any possibility for the deployment of Indian troops to Afghanistan.
Her statement came during a joint press conference with US Defense Secretary James Mattis in New Delhi.
Sitharaman reaffirmed that India would continue providing development assistance to Afghanistan.
Sitharaman and Mattis also agreed that India and the US would eradicate terrorist safe havens globally.