Within the European Union’s borders, visas are not required.
Citizens of the following countries can travel to Poland without a visa:
Andorra, Argentina, Australia, Austria, Belgium, Brazil, Brunei, Bulgaria, Canada, Chile, Costa Rica, Croatia, Cyprus, the Czech Republic, Denmark, El Salvador, Estonia, Finland, France, Germany, Greece, Guatemala, Honduras, Hong Kong (special administrative region), Hungary, Iceland, Ireland, Israel, Italy, Japan, Latvia, Liechtenstein, Lithuania, Luxembourg, Macao (special administrative region), Malaysia, Malta, Mexico, Monaco, the Netherlands, New Zealand, Nicaragua, Norway, Panama, Paraguay, Portugal, Romania, San Marino, Singapore, Slovakia, Slovenia, South Korea, Spain, Sweden, Switzerland, the United Kingdom, the United States of America, Uruguay, the Vatican, Venezuela.
Visas are required for citizens of Russia, Belarus and Ukraine.
Since December of 2007, Poland has been a member of the Schengen Agreement. For the whole territory of the Schengen Agreement, there is no passport control at the borders. Anyway, it’s always required to carry ID when travelling abroad.
These are the countries of the Schengen Zone:
Austria, Belgium, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Italy, Latvia, Lithuania, Luxembourg, Malta, Monaco, the Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden.
Two members of the EU are not members of the Schengen Agreement: Great Britain and Ireland.
Detailed information about visas: http://www.msz.gov.pl/Visa,requirements,2346.html