As a British citizen, you don't need a visa to enter Poland if you're in the country for less than 3 months. But, your passport must be valid for the duration of your stay.
As a US national, you must have a valid passport to travel to this destination and it is advisable that your passport is valid for the duration of your stay. Moreover, we always recommend having a return airline ticket, in case you are stopped at border control. Your maximum stay must be less than 3 months, unless you have a visa.
Poland is inside the Schengen area, which means that you won't need a visa to enter the country if you are staying under 90 days. Note, that your passport is valid for at least six months from the date you intend to return.
EU, EEA and Swiss citizens
If you are from an EU member state or from countries in the European Economic Area, you will not need a visa to visit Poland.
EU member countries
Germany, Austria, Belgium, Bulgaria, Cyprus, Croatia, Denmark, Slovakia, Slovenia, Spain, Estonia, Finland, France, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Poland, Portugal, United Kingdom, Czech Republic, Romania and Sweden.
Island, Liechtenstein and Norway.
Citizens of the following countries do not need a visa to enter Ireland
The following countries do not require a visa for visits lasting less than 90 days, but require a valid passport to enter Poland.
Andorra, Antigua & Barbuda, Argentina, Australia, Austria, Bahamas, Barbados, Belgium, Belize, Bolivia, Botswana, Brazil, Brunei, Bulgaria, Canada, Chile, Costa Rica, Croatia, Cyprus, Czech Republic, Denmark, Dominica, El Salvador, Estonia, Fiji, Finland, France, Germany, Greece, Grenada, Guatemala, Guyana, Honduras, Hong Kong, Hungary, Iceland, Israel, Italy, Japan, Kiribati, Latvia, Lesotho, Liechtenstein, Lithuania, Luxembourg, Macau, Malaysia, Maldives, Malta, Mexico, Monaco, Nauru, Netherlands, New Zealand, Nicaragua, Norway, Panama, Paraguay, Poland, Portugal, Romania, Saint Kitts & Nevis, Saint Lucia, Saint Vincent & the Grandines, Samoa, San Marino, Seychelles, Singapore, Slovakia, Slovenia, Solomon Islands, South Africa, South Korea. Spain, Switzerland, Taiwan, Tonga, Trinidad & Tobago, Tuvalu, United Kingdom, United States, Uruguay, Vanuatu, Vatican City
If your country has not been mentioned previously, please check the official website of the Ministry of Foreign Affairs of the Republic of Poland.