Before the 20th century, the term "Sejm" referred to the entire three-chamber Polish parliament, comprising the lower house (Chamber of Envoys; Polish: Izba Poselska), the upper house (Senate; Polish: Senat) and the King. It was commonly termed a three-estate parliament. Since the Second Polish Republic (1918-1939), the term "Sejm" has referred only to the lower house of the parliament; the upper house is called the "Senat".
The power of early, various wiece ("councils") grew stronger during the time of Poland's fragmentation (1146-1295), but it was only in the late 15th century that the Sejm became established as a regularly convening body. From 1493 forward, the indirect elections were repeated every two years. With the development of the unique, Polish "Golden Liberty" system, the Sejms powers increased.
The first Sejm was composed of two chambers:
The number of envoys in the lower chamber grew in number — and power — as they pressured the king for more privileges. The spur toward action increased when landed nobility was drafted into military service. After 1569's Union of Lublin, the Kingdom of Poland was transformed into the federation of the Polish-Lithuanian Commonwealth, and the number of the Sejms members was increased by including envoys from the Lithuanian nobility.
The Sejm severely limited the king's powers. Its chambers reserved the final decisions in legislation, taxation, budget, and treasury matters (including military funding), foreign affairs, and titles of nobility. In 1573, in the act of the Warsaw Confederation, the nobles of the Sejm officially sanctioned, and guaranteed to each other, religious tolerance in Commonwealth territory, ensuring an eastern-European refuge from the ongoing Reformation and Counter-Reformation wars.
Until the end of the 16th century, unanimity was not required, and the majority-voting process was the most commonly used electoral form. Later, with the rise of power held by Polish magnates, the unanimity principle was reinforced with the institution of the nobility's right of liberum veto (Latin for "I freely forbid"). If the envoys were unable to reach a unanimous decision within six weeks (the time limit of a single session), deliberations were declared null and void. From the mid-17th century onward, any objection to a Sejm resolution — by either an envoy or a senator — automatically caused the rejection of other, previously approved resolutions. This was because all resolutions passed by a given session of the Sejm formed a whole resolution, and, as such, was published as the annual constitution of the Sejm, e.g., Anno Domini 1667. In the 16th century, no single person or small group dared to hold up proceedings, but, from the second half of the 17th century, the liberum veto was used to virtually paralyze the Sejm, and brought the Commonwealth to the brink of collapse. The liberum veto was finally abolished by the May Constitution of Poland in 1791.
It is estimated that, between 1493 and 1793, sejms were held 240 times, with a debate-time sum of 44 years.
Parliament of the Kongresówka , or Congress Poland, was composed of the king, the upper house (Senate), and the lower house (Chamber of Envoys).
The Chamber of Envoys, despite its name, consisted not only of 77 envoys (sent by local assembly) from the hereditary nobility, but also of 51 deputies, elected by the non-noble population. A deputy's term of office was six years; half of the deputies were elected every two years, and all were covered by Parliamentary immunity. Candidates for deputy had to be able to read and write, and have a certain amount of wealth. The legal voting age was 21, but military personnel were not allowed to vote.
Parliamentiary sessions were initially convened every two years, and lasted for (at least) 30 days. However, after many clashes between liberal deputies and conservative government officials, sessions were later called only four times (1818, 1820, 1826, and 1830, with the last two sessions being secret).
The Sejm had the right to call for votes on civil and administrative legal issues. With permission from the king, it could also vote on matters related to the fiscal system and the military. It had the right to control government officials, and to file petitions.
The 64-member Senate was composed of voivodes and kasztelans (both types of provincial governors), Russian "princes of the blood," and nine bishops. It acted as the Parliament Court, had the right to control citizens' books, and had similar legislative rights as did the Chamber of Deputies.
During the interwar period of Poland's independence, the first Sejm in 1919 passed the Small Constitution of 1919, which introduced a parliamentary-republic system, which was strengthened, in 1921, by the March Constitution of Poland. In 1926 and 1935, the republic was weakened by Józef Piłsudski's May Coup, and, particularly, the Polish Constitution of 1935, respectively.
The Sejm in the People's Republic of Poland had 460 deputies throughout most of its history. At first, this number was declared to represent one deputy per 60,000 citizens (425 were elected in 1952), but, in 1960, as the population grew, the declaration was changed: The constitution then stated that the deputies were representative of the people and could be recalled by the people — but this article was never used, and, instead of the "five-point electoral law," a non-proportional, "four-point" version was used. Legislation was passed with majority voting.
The Sejm voted on the budget as well as on the periodic "national plans" that were a fixture of communist economies. The Sejm deliberated in sessions that were ordered to convene by the State Council.
The Sejm also chose a Prezydium ("presiding body") from among its members; the marshall of which was always a member of the United People's Party. In its preliminary session, the Sejm also nominated the Prime Minister, the Council of Ministers of Poland, and members of the State Council. It also chose many other government officials, including the head of The Supreme Chamber of Control and members of the State Tribunal and the Constitutional Tribunal, as well as the Ombudsman (the last three bodies of which were created in the 1980s).
After the fall of communism in 1989, the Senate was reinstated as the upper house of a bicameral national assembly, while the Sejm became the lower house. The Sejm is now composed of 460 deputies elected by proportional representation every four years.
Between 7 and 19 deputies are elected from each electorate using the d'Hondt method (with one exception, in 2001, when the Sainte-Laguë method was used) — their number being proportional to an electorate's population. Additionally, a threshold is used, so that candidates are chosen only from parties that gained at least 5% (8% for registered coalitions) of the nationwide vote (candidates from ethnic-minority parties are exempt from this threshold).