Look at the
visa requirements by country to see if you need a visa to visit Brazil.
Note that this list may change, and without notice of course. Most Europeans and South Americans do
not need a visa to visit Brazil. Those travelling with a US passport will
need a visa. Attendees and/or unpaid speakers (daily allowances paid by Brazilian sources are permitted) in conferences should apply for a tourist visa and one can find the necessary requirements
here. The Brazilian consulates in the US do not accept visa applications by mail. One either has to apply in person, or by proxy
( e.g. ask a friend to respresent you or hire a visa agency).
A list of the Brazilian Consulates in the US and their respective
jurisdictions can be found at
List of Consulates in the US.