Among the earliest recognised formal legislatures was the Athenian Ecclesia. In the Middle Ages, European monarchs would host assemblies of the nobility, which would later develop into predecessors of modern legislatures. These were often named the Estates. The oldest surviving legislature is the Icelandic Althing, founded in 930 CE.

Democratic legislatures have six major functions: representation, deliberation, legislation, authorizing expenditure, making governments, and oversight.
There exist five ways that representation can be achieved in a legislature:
• Formalistically: how the rules of the legislature ensure representation of constituents;
• Symbolically: how the constituents perceive their representatives;
• Descriptively: how well the composition of the legislature matches the demographics of the wider society;
• Substantively: how well representatives actually respond to the needs of their constituents;
• Collectively: how well the representatives represent the interests of the society as a whole.
One of the major functions of a legislature is to discuss and debate issues of major importance to society. This activity can take place in two forms. In debating legislatures, such as the Parliament of the United Kingdom, the floor of the legislature frequently sees lively debate. In contrast, in committee-based legislatures like the United States Congress, deliberation takes place in closed committees.
While legislatures have nominally the sole power to create laws, the substantive extent of this power depends on details of the political system. In Westminster-style legislatures the executive (composed of the cabinet) can essentially pass any laws it wants, as it usually has a majority of legislators behind it, kept in check by the party whip, while committee-based legislatures in continental Europe and those in presidential systems of the Americas have more independence in drafting and amending bills.
The origins of the power of the purse which legislatures typically have in passing or denying government budgets goes back to the European assemblies of nobility which the monarchs would have to consult before raising taxes. For this power to be actually effective, the legislature should be able to amend the budget, have an effective committee system, enough time for consideration, as well as access to relevant background information.
There are several ways in which the legislature can hold the executive branch (the administration or government) accountable. This can be done through hearings, questioning, interpellations, votes of confidence, the formation of committees. Parliaments are usually ensured with upholding the rule of law, verifying that public funds are used accountably and efficiently as well as make government processes transparent and actions so that they can be debated by the public and its representatives.

Agora notes that parliamentary systems or political parties in which political leaders can influence or decide which members receive top jobs can lead to passivity amongst members of the party and less challenging of leadership. Agora notes that this phenomenon is acute if the election of a member is dependent on the support of political leadership.
In contrast to democratic systems, legislatures under authoritarianism are used to ensure the stability of the power structure by co-opting potential competing interests within the elites, which they achieve by:
• Providing legitimacy;
• Incorporating opponents into the system;

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Each chamber of the legislature consists of a number of legislators who use some form of parliamentary procedure to debate political issues and vote on proposed legislation. There must be a certain number of legislators present to carry out these activities; this is called a quorum.

Some of the responsibilities of a legislature, such as giving first consideration to newly proposed legislation, are usually delegated to committees made up of a few of the members of the chamber(s).

The members of a legislature usually represent different political parties; the members from each party generally meet as a caucus to organize their internal affairs.