Projected Population in 2015: 18.6 million
Population in 2005: 15 million

Delhi was the capital of the Mughal emperors, whose Red Fort still broods over the center of the city. The British took over in 1857 and later built the New Delhi government complex, which has served as India's capital since independence. Mumbai may have Bollywood, and Bangalore may style itself India's Silicon Valley, but Delhi still exudes the old imperial glamour. As a seat of power, it has been attracting migrants for centuries, and they're still coming today.