The Visa Waiver Program allows citizens of participating countries to travel to the United States without a visa for stays of 90 days or less. This is only if they they meet all requirements explained below. Travelers must be eligible to use the VWP and have a valid Electronic System for Travel Authorization (ESTA) approval prior to travel.
If you are eligible to travel on the VWP, but prefer to have a visa in your passport, you may still apply for a visitor (B) visa. Transiting or traveling through the United States to Canada or Mexico is generally permitted for VWP travelers.