You may need a U.S. visa if you are planning to enter the United States for a purpose other than tourism or business for stays of 90 days or less. Generally, a U.S. visa is required for individuals who plan to:

• Live, work, or study in the United States: If you plan to work or study in the United States, you will need to apply for a nonimmigrant visa, such as a H-1B visa for skilled workers, an F-1 visa for students, or an J-1 visa for exchange visitors.
• Visit the U.S. for reasons other than tourism or business: If you plan to visit the U.S. for reasons such as medical treatment, performing in a concert, or taking part in a competition, you will need to apply for a B-1/B-2 visitor visa.
• Apply for permanent residence: if you are planning to immigrate and apply for permanent residence in the U.S. (a green card) you will need to obtain an immigrant visa.
• Traveling to the U.S. from a country that is not part of the Visa Waiver Program (VWP) : Citizens of countries that are not part of the VWP, such as Iran, North Korea, Syria, and many others need to obtain a visa to enter the U.S.

It’s worth noting that if you are a citizen or national of a  ESTA Visa Waiver Program (VWP) country and planning to travel to the U.S for tourism or business for stays of 90 days or less, you may not require a visa, but you will need to obtain an ESTA (Electronic System for Travel Authorization) before traveling.

If you are unsure of the type of visa you need, or if you have any questions about your eligibility to travel to the United States, it’s recommended to contact the U.S. embassy or consulate in your country, they will be able to provide you with more information and assist you in the application process for a visa.