I'm traveling to Mumbai from Atlanta,Ga. I'm landing at 8:45pm and returning back the same night at midnight. Do I need anything other than a US passport? Thanks!

Assuming you are a US citizen - you will need a visa to get through passport control. Even though you may not be leaving the airport grounds, I doubt that you can get back to the boarding area for the return flight without going through passport control.

Assuming you are US citizen, you need a visa.. contact the embassy:

India Embassy , United States
2107, Massachusetts Avenue, NW
20008 Washington D.C
District of Columbia USA
Phone: +1-202-9397000
Fax: +1-202-2654351
Email: [email protected]
[email protected]
Website URL: www.indianembassy.org