Legislatures do a lot of different things, but their primary jobs are to make laws, represent constituents, and oversee other parts of government. These jobs exemplify the fundamental reasons a political system needs a legislature. When the people empower a branch of the political system to make the rules governing their relationship with their government, the political system is equipped to resist the ways that power can corrupt. Legislative institutions must require cooperation and consensus to ensure the health of the political system.
At the national level, there are two primary types of governing systems, parliamentary and presidential. The largest difference between the two types of systems relates to the relationship between the legislative and executive branches of government. In a parliamentary system, the executive power, or the power to see that the laws are followed, is vested in a prime minister, who is also the head of the legislative branch. This means that power flows from the people to the legislature and then from the legislature to the executive. In a presidential system, the executive, usually in the form of a president, is completely separate from the legislature. The people separately elect the legislature and the executive, so the power flows from the people to the legislature and from the people to the executive.
There are also two primary types of organizing systems in legislatures. First, there are legislatures with only one chamber, which are called unicameral. Second, there are legislatures with two chambers, called bicameral legislatures. Unicameral legislatures are thought to be more efficient than bicameral legislatures, but bicameral legislatures are designed to take into account a variety of different viewpoints.
Legislatures face a number of challenges to their power and independence. Some of those challenges are external, such as executive dominance, in which the growing power of presidents and prime ministers threatens to overtake the power of the legislature. Other threats are internal, particularly legislative deference, in which because of either an inability to come together and act or a desire to avoid difficult issues, the legislature gives up power to other branches. Finally, some threats are systemic, such as increasing polarization, which has shown up both in the public and in legislatures. Without considering the threats to the legislature, it is impossible to understand the full scope of its work and its place in the political system.