The concordat is a legal instrument, which enables peaceful and harmonious regulation of mutual relations between the State and the Catholic Church. With regard to Poland – excluding partial convensions concluded with the Holy See in the period of the First Polish Republic – the first concordat regulating all issues concerning mutual relations between the Polish State and the Catholic Church was only concluded in the Second Polish Republic: February 10, 1925, shortly after regaining independence. The Concordat regulated all legal and constitutional status of the Catholic Church in the Second Polish Republic (excluding matters left to be settled in separate agreements, for example the question of marriages and registry office records acts). Concordat, which consists of 27 articles contains a concise preamble, then general rules, provisions relating to the particular matters regarding both parties and final arrangements. There is no doubt, that the Concordat of 1925 concluded with Poland was one of the best agreements, that the Holy See concluded in the interwar period. The outbreak of Second World War of 1939 – only 14 years after the conclusion of the Concordat – made the beginning of the implementation process of its provisions drastically interrupted.