Sejm of the Polish–Lithuanian Commonwealth

The general sejm (Polish: sejm walny, also translated as the full or ordinary sejm) was the bicameral parliament of the Polish–Lithuanian Commonwealth. It was established by the Union of Lublin in 1569 from the merger of the Sejm of the Kingdom of Poland and the Seimas of Grand Duchy of Lithuania, Ruthenia and Samogitia. It was one of the primary elements of the democratic governance in the Commonwealth (see Golden Liberty). The sejm was a powerful political institution and the king could not pass laws without the approval of that body.

Duration and frequencies of the sejms changed over time, with the six-week sejm session convened every two years being most common. Sejm locations changed throughout history, eventually with the Commonwealth capital of Warsaw emerging as the primary location. The number of sejm deputies and senators grew over time, from about 70 senators and 50 deputies in the 15th century to about 150 senators and 200 deputies in the 18th century. Early sejms have seen mostly majority voting, but beginning in the 17th century, unanimous voting became more common, and 32 sejms were vetoed with the infamous liberum veto, particularly in the first half of the 18th century. This vetoing procedure has been credited with significantly paralyzing the Commonwealth governance.

In addition to the regular sessions of the general sejm, in the era of electable kings, beginning in 1573, three special types of sejms (convocation, election, and coronation sejms) handled the process of the royal election in the interregnum period. In total, 173 sejms met between 1569 and 1793.

The word sejm and sejmik are derived from old Czech sejmovat, which means "to bring together" or "to summon". In English, the terms general, full or ordinary sejm are used for the sejm walny.

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