It has been a longstanding tradition that the organizers of the ICM offer support in order that mathematicians from developing countries can participate at the ICM.
For the ICM 2018 in Rio de Janeiro, Brazil, the organizers have generously announced the ICM2018 Open Arms Program that will grant 550 travel awards, 200 of which to mathematicians working in countries in Latin America other than Brazil. The program is sponsored by IMPA (Instituto Nacional de Matemática Pura e Aplicada) and the Brazilian Mathematical Society, alongside with a generous offer of 50 travel grants from the International Mathematical Union. Applications to the program will be open from April 15 to July 20, 2017.
See
http://www.icm2018.org/portal/en/travel-grants-program
for further details and deadlines.