Useful links :

Customs Service Official Website :
http://www.mf.gov.pl/sluzba-celna

The EU Customs Code  :
https://ec.europa.eu/taxation_customs/business/union-customs-code_en 

Customs Service of the Republic of Poland – System ISZTAR – Tariff Information :

http://isztar.mf.gov.pl/isztar/taryfa_celna/web/main_EN

Poland – Customs Regulations :

https://www.export.gov/article?id=Poland-Customs-Regulations

Ministry of Foreign Affairs Republic of Poland – CUSTOMS INFORMATION

https://mfa.gov.pl/en/travel_to_poland/customs_info/