At least one British national, a Japanese, and an Australian were among the 104 people killed.
Some hostages have been freed, but others--including eight Israelis in a Jewish outreach center--are still being held.
The Indian PM claims the attackers were based "outside the country" and says that India will not tolerate "neighbors" harboring such militants.
Experts question the existence of the "Deccan Mujahedeen," which has claimed responsibility for the attacks, but caution against jumping to the conclusion that Al-Qaeda is responsible.
Speculation about the attackers' identity has centered around Indian Mujahedeen, a domestic Muslim terrorist group, and Lashkar-e-toiba, a Pakistan-based guerilla group active in Kashmir.
The Los Angeles Times notes that some 2,300 people in India died last year in attacks by various groups, making it "perhaps the country most affected by terrorism in the world."
Mumbai residents used Twitter, Flickr, and other social media to broadcast information about the attacks.
UPDATE: The eight hostages at Mumbai's Chabad center have been freed, Ha'aretz reports. But 20-30 Israelis are among those still being held in a separate siege at the Trident-Oberoi hotel.