All information about entry requirements to the Czech Republic can be found at pagews of the Ministry of Foreign Affairs (http://www.mzv.cz/jnp/en/information_for_aliens/index.html).
Residents of the European Union Member States, as well as of Switzerland, Norway, Liechtenstein and Iceland are not required to have a visa and may enter the Czech Republic with a valid passport or identification card.
The List of States the citizens of which are exempt from visa requirement to enter the Czech Republic: http://www.mzv.cz/jnp/en/information_for_aliens/short_stay_visa/list_of_states_whose_citizens_are_exempt/index.html
The List of States the citizens of which are required to have visa to enter the Czech Republic: http://www.mzv.cz/jnp/en/information_for_aliens/short_stay_visa/list_of_states_whose_citizens_are/index.html
The visa shall be obtained from the Czech embassies abroad. Further information on visas: http://www.mzv.cz/jnp/en/information_for_aliens/index.html,
Specially for Russian competitors information from Moscow embassy in russian language: http://www.mzv.cz/moscow/ru/vizy_i_konsulskaja/vizovaja/schengenskaja/dlja_kultury_sporta.html
All ERC 2015 participants who need a letter of invitation in order to get the Czech visa can ask organisers via email (firstname.lastname@example.org) until 30th April 2015 - Please provide us with your full name and your passport number with which you will ask for visa. We will send you back an invitation letter.