If you are outside the U.S and planning to attend a conference in the USA, you must determine whether you need a visa to enter the USA.

The appropriate visa status for conference attendees is "B-1 Business Visitor." This allows temporary entry to the United States for business purposes like attending conferences, seminars, or professional conventions.

For most individuals, a B-1 visa must be obtained from a US Consulate. Once issued, a “B” visa might be valid for up to 10 years for entering the US to engage in qualifying activities (such as conference attendance). However, the USA has a “Visa Waiver Program” (VWP) which permits citizens of certain countries to enter the USA in B-1 Business Visitor status, but without first obtaining the physical visa from a US Consulate. Instead, qualifying applicants obtain a screening approval using the US “ESTA” system to enter the US without the “B” visa in hand.

If you are unsure whether you need to obtain a B-1 Business Visitor visa or use the Visa Waiver Program, use the U.S. Department of State’s Visa Wizard to find out which you should apply for. Be sure to select “Business” as the purpose for your travel to the USA, if the trip is for purposes of attending a conference or workshop. “Visits” are normally associated with tourism activities. “Employment” refers only to entering the US to engage in labor or services for a US person or organization.

If you have determined that you do need a business visitor visa, review the instructions provided by the State Department in terms of where and how to apply.

In general, there are four steps:

The U.S. Department of State requires business visitor visa applicants to attend an in-person interview. You may use the “Visa Wait Times” tool on the Department of State website to calculate the number of days between the submission of your application (Form DS-160) and the interview. To use the tool, you must select the city where the US Consulate you will apply at is located. The wait time between Step 1 and Step 2 consumes the largest portion of the total processing time to obtain a visa, so the number of days you see in the Visa Wait Times tool will be a good indication of whether the visa will be issued in sufficient time for your travel. Some consulates have extremely long wait times for “business visitor” interviews. If the Visa Wait Times tool indicates “999” as the number of days, that means that the Consulate is not accepting business visitor visa applications at this time.

If you are located within geographic reach of more than one US Consulate, you may check sequential visa wait times by click on the red square with the pencil in it to clear your prior selection. Note, though, that you should have a “legitimate” purpose for visiting a third country beyond applying for a visa at the US Consulate there; US consulates frown on “consulate shopping” solely to find the shortest processing time.

The US Department of State maintains a list of the countries that are approved to participate in the US Visa Waiver Program. Citizens of (only) these countries are eligible to apply for admission to the US without first obtaining a “business visitor” (or tourist) visa.

To be eligible for admission under the US Visa Waiver Program, individual travelers must have valid Electronic System for Travel Authorization (ESTA) approval prior to boarding an inbound US air or sea carrier, or attempting to cross a land border. ESTA is a web-based system operated by U.S. Customs and Border Protection (CBP) to determine eligibility to travel to the United States for tourism or business under the US Visa Waiver Program.

There are two steps to obtaining an ESTA approval:

You can review more information about ESTA, and submit your application for ESTA approval, on the government's ESTA webpage. If approved, the authorization is valid for two years or until the traveler’s passport expires, whichever comes first. ESTA is not conference- or visit-specific; once ESTA is approved for a visit, the same ESTA authorization may be used for subsequent visits to the US during the validity of the approval.

A letter of invitation normally is a required element in support of a “business visitor” visa application to the US Consulate.

Similarly, both visa-holders and Visa Waiver travelers often find it useful to have documentation about the conference, such as a registration and/or letter of invitation, to present to the Customs and Border Protection (CBP) officers that perform the immigration and admission clearances during pre-flight inspection and/or after arrival in the USA.

As a result, many (but not all) international conference attendees might want to request a letter of invitation. To request an invitation letter, please submit your request by email to the Purdue University contact for your specific conference or workshop. They will coordinate the issuance of the letter once Purdue University has approved your attendance, as follows:

• Screening by Purdue University’s Office of Research Compliance is automatically undertaken for all international conference attendees. This is initiated based on your registration. It is performed in bulk, at certain times during the registration process; it is not triggered by or in reaction to your specific registration. Decisions will be conveyed via email. Purdue University will not provide explanations of why screening was denied, if this occurs.
• Once screening is approved, the Purdue University contact for your conference is permitted to coordinate the issuance of the letter of invitation. The letter template used for all invitations is based on Purdue policy and cannot be changed pursuant to individual requests or circumstances. Your Purdue University conference contact can provide you with more specific information about how and when letters will be issued.
• The Letter of Invitation will ONLY be sent via email to the email address that you provide. The Letter of Invitation cannot be emailed or sent to the Embassy or U.S. Consulate.
• In general, because of the lengthy time to obtain consular interviews, if you are applying for a “business visitor” visa, we recommend that you submit your Form DS-160 application at the earliest possible moment provided that you also accommodate the estimated letter issuance timeline given to you by your Purdue University conference contact. Include your conference registration if the application process asks for documentation of the purpose of the visit. The invitation letter may be supplied at the time of interview.
• ISS does not assist with the issuance of invitation letters for conference and workshop attendees.

Note: if you have a pre-existing B visa or ESTA approval, and you do not feel you need to present conference-specific invitation or documentation during pre-flight or post-arrival inspection, then you do not need to request an invitation letter.

It is your responsibility to ascertain the method by which you will enter the USA and obtain whatever documents you need for this admission, as far in advance as possible. Purdue University and most conferences will not refund registration fees after the registration cut-off date due to an individual's inability to obtain a visa, ESTA approval, or admission to the US. Purdue University will not intervene on behalf of the invitees with the Embassy or U.S. Consulate, or with the US Customs and Border Protection office.