This is what we found on Wikipedia regarding the Polish Club:

Polish Club (Polish: Wspólny Język, literally "Common Language") is a bridge bidding system which was developed in Poland, where it is the most popular bidding system, and which is also used by players of other countries. It is a type of small club system.

In the Polish Club, a 1♣ opening bid is forcing for one round but does not necessarily show a strong hand; in most versions of this system it shows either a weak balanced hand (about 12-14HCP), a natural 1♣ opening or any strong hand. Consequently, bids of 1♦, 1♥ and 1♠ are limited to about 18HCP, and also 1♦ shows at least four diamonds (five in some versions of the system).

The 2♣ opening is usually reserved to show a limited hand with long clubs and possibly a four-card major, similar to the Precision 2♣ opening.

The following outline of the system is based on that given in System licytacyjny Wspólny Język 2005 - opis skrócony ("Polish Club 2005 - a brief description") by Krzysztof Jassem. The latest version translated into English (Polish Club International, 2010), is available here: