The bride, Isha Ambani, is the Ivy League-educated daughter of industrialist Mukesh Ambani, thought to be India's richest man. Forbes estimates his net worth at over $43 billion.
The groom, Anand Piramal, is the relative pauper. His father, industrialist Ajay Piramal, is thought to be worth $10 billion.
The wedding is being held in Mumbai on Wednesday but festivities began weeks ago, starting in September with an engagement party at a lakeside Italian palace.
Over the weekend, thousands attended pre-wedding parties at a 16th century palace in the Indian desert city of Udaipur, where videos shot by partiers showed Hillary Clinton dancing with Shah Rukh Khan, one of India's biggest movie stars, as former U.S. Secretary of State John Kerry danced just a few feet away.
A highlight was a performance by Beyonce, who sang "Crazy In Love," among other hits, with a band backing her up and a series of costume changes that included at least one India-inspired outfit.