If you are coming to Orlando, Florida, USA from another country, you might need a visa; please read on. (The following information is taken directly from the U.S. Department of State website.)
What is a U.S. Visa?
A citizen of a foreign country who seeks to enter the United States generally must first obtain a U.S. visa, a travel document issued by the traveler’s country of citizenship, which is then placed in the traveler’s passport.
Certain international travelers may be eligible to travel to the United States without a visa if they meet the requirements for visa-free travel. Click Here for More Important Visa Information. (This link contains information about U.S. visas for foreign citizens that you'll need to travel to the United States.)
How Can I Use a Visa to Enter the United States?
Having a U.S. visa allows you to travel to a port of entry, airport, or land border crossing, and request permission of the Department of Homeland Security (DHS), Customs and Border Protection (CBP) inspector to enter the United States. While having a visa does not guarantee entry to the United States, it does indicate a consular officer at a U.S. Embassy or Consulate abroad has determined you are eligible to seek entry for that specific purpose. DHS/CBP inspectors, guardians of the nation’s borders, are responsible for admission of travelers to the United States, for a specified status and period of time. DHS also has responsibility for any immigration matters you may encounter while present in the United States.
More information can be found at the State Department's FAQ, here.
Do I need a Visa?
Please study the U.S. Department of State website (click here) to learn more about visas. Access the “visa-wizard” here for help determining which visa you need.
Invitation Letters from the National Space Society
You may also need an invitation letter. An invitation letter is required before applying for a visa. In order to attend the ISDC as a visitor from another country, you may need to obtain an invitation letter from the NSS. (If you will require a visa to enter the U.S., you must have this letter.) If you are attending in connection with an NSS space contest, such as the Gerard K. O'Neill Space Settlement Contest or the "Live in a Healthy Space" Design Competition, please use the Contest online form. For general ISDC attendees, please request your invitation letter using the Non-Contest online form.