Generally, a citizen of a foreign country who wishes to enter the United States must first obtain a visa. Visitor visas are nonimmigrant visas for persons who want to enter the United States temporarily for business (visa category B-1), tourism, pleasure or visiting (visa category B-2), or a combination of both purposes (B-1/B-2).
Attending a scientific, educational, professional, or business convention or conference falls under the category of B-1.
There are several steps to apply for a visa. We encourage you to begin that process. Please visit https://travel.state.gov/content/visas/en.html to learn more about applying for a visa.