No, you do not have to be a US citizen to attend, and we strongly encourage international citizens to apply. Most European citizens are eligible to enter the US under the ESTA Visa Waiver Program to attend a conference. The application for a Visa Waiver is relatively short and can be done up until the week of travel. You may also apply for or acquire a B1 or B2 visa relatively short. For example, Canadians passport holders can acquire a B1/B2 visa upon their departing flight into the US. Future Forum does not give recommendations for US visa application processes and we would recommend you visit this link for more information regarding the visa waiver program and this link for visitor visas.