If you are traveling to the meeting from outside the United States, SSA recommends that you start the process of applying for a visa at least three months prior to the meeting. Security-related policies have greatly increased the processing time for visa applications.
Visa Waiver Program (VWP): Please note that the State Department has required citizens from VWP countries to obtain visas if they do not have machine-readable passports. One-time exemptions are no longer available to VWP nationals who do not possess a machine-readable passport or a non-immigrant visa.
Letters of invitation can be requested by sending your name, address, SSA membership ID number and a description of how you plan to participate in the meeting to firstname.lastname@example.org. If you want specific information included in your letter, please let us know. Letters are required for most visa processes.
The National Academies of Sciences maintains a website about visa-related issues and travel information for U.S. citizens and non-U.S. citizens.