thumb|350px|Sejm during the reign of [[Sigismund III Vasa (1587–1632)]]
thumb|350px|Sejm during the reign of [[Augustus II the Strong (1694–1733)]]
The General Sejm (, ) was the bicameral legislature of the Polish–Lithuanian Commonwealth. It was established by the Union of Lublin in 1569 following the merger of the legislatures of the two states, the Sejm of the Kingdom of Poland and the Sejm of the Grand Duchy of Lithuania. It was one of the primary elements of the democratic governance in the Commonwealth (see Golden Liberty). The sejm was a powerful political institution. The king could not pass laws without its approval.
The two chambers of a sejm were the Senate (senat) consisting of high ecclesiastical and secular officials, and the lower house, (izba poselska), the sejm proper, of lower ranking officials and the representatives of all szlachta. Together with the king, the three were known as the sejming estates, or estates of the sejm (stany sejmujące, literally, "deliberating estates").
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 liberum veto provision, particularly in the first half of the 18th century. This vetoing device 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.
Political influence
thumb|250px|right|The first Polish royal election, of [[Henry III of France|Henry III Valois, took place in 1573]]
Sejms, including their senate (the upper chamber), and sejmiks severely limited the king's powers.
Already the Sejm of the Kingdom of Poland has a great impact on the king's powers. From 1505 the king could not pass laws himself without the approval of the sejm, this being forbidden by Polish szlachta privilege laws like nihil novi. Usually larger voivodeships could send 6 deputies, smaller 2; ziemias, depending on their sizes, would send 2 or 1. The Grand Chancellor of Lithuania and Vice-Chancellor of Lithuania were regarded as guardians of the laws and were obliged to refuse to affix the Lithuanian seals to any documents that would violate the laws or act to the detriment of the state.
Location
thumb|[[New Grodno Castle, where most of the federal Polish–Lithuanian sejms in the territory of Lithuania were held, including the last one in 1793]]
The majority of the sejms were held at the Warsaw's Royal Castle. In practice, most of the sejms were still held in Warsaw, which hosted 148 sejms, compared to 11 sejms hosted in Grodno. Polish–Lithuanian monarch Augustus III even described Grodno as "hated small town" and Polish nobles reluctantly travelled to the federal Polish–Lithuanian sejms in Grodno. In his welcoming speech during the 1784 Grodno Sejm Kazimierz Nestor Sapieha mildly reproached Poniatowski that "It has been thirty-two years already that Lithuania did not see legislative meetings in its nest".
The sejms in Warsaw were held in the Warsaw Castle, within the Chamber of Deputies (Hall of Three Pillars), with the upper Senate Chamber located literally above it. Jędruch gives a higher number of 245, and notes that 192 of those were successfully completed, passing legislation.