Conference participants may be required to obtain a visa to enter Brazil. Many International visitors to Brazil, including those coming from most EU and Latin-American countries are are eligible for visa exemptions, and may travel to Brazil with a valid passport. Visitors from countries including the United States, Canada, and China must obtain a Vitur visa before traveling to Brazil.
Please see this document to determine if you need a travel visa. Find the line for your country, and check the Vitur (Tourism Visa) column. A value of 1 in this column indicates that a visa is required, and a value of 8 indicates a visa exception for up to 90 days of travel.