Poland has been part part of the Schengen Area since 2007. The Schengen Area is a territory consisting of 28 countries without controls of internal borders. The only thing that participants coming from this zone will need is a valid ID card. There is also no visa requirements for citizens of several other countries not belonging to Schengen, as long as they do not intend to stay in the EU for longer than 90 days (here is the full list of them). Those who need to apply for a visa should visit the page of the Ministry of Foreign Affairs Republic of Polandwhere exact information on the visa application process can be found. You can also contact the Polish Embassy or Consulate situated closest to you (here). Please make sure before starting the whole procedure that your passport is valid and has enough space for a new visa.