According to the Delaware Department of State*:
More than half a million business entities have their legal home in Delaware including more than 50% of all U.S. publicly-traded companies and 58% of the Fortune 500. Businesses choose Delaware because we provide a complete package of incorporation services including modern and flexible corporate laws, our highly-respected Court of Chancery, a business-friendly State Government, and the customer service oriented Staff of the Delaware Division of Corporations.
Here are some of the reasons that Delaware is the most favored state for incorporation: