There are a number of differences between Congress, the Senate and the House of Representatives, but they all function as the legislative branch of the federal government. Essentially, Congress generates potential laws in a form known as a bill. A bill may start in the House of Representatives or the Senate, but it is not usually presented to the executive branch, i.e. the president, until both houses have worked out their differences over wording and intention of the proposed law.

When referring to the entire legislative branch, the proper collective term is Congress. Unlike the people who serve in the Senate or House of Representatives, the Congress as a whole exists for one year at a time. Historians may refer to the 87th Congress, for example, meaning those Senate and House members who met during that particular year. In that sense, "Congress" is a year-long event, while the Senate and House of Representatives buildings have existed for many decades.

Within the Congress are two separate entities known as the Senate and the House of Representatives, roughly the equivalent of Great Britain's House of Lords and House of Commons. A legislative body with two separate chambers, such as the United States Congress, is said to be bicameral.

One noticeable difference between the two houses of Congress is the number of members. The House of Representatives currently contains 435 members, one from each of 435 districts which represent portions of the states. States with a higher population are allotted more representatives than less populated states. These representatives serve two-year terms, meaning they could be up for re-election during every other Congress. The Senate, on the other hand, has 100 members, two from each state regardless of population. Senators serve six-year terms, with no term limitations.

Another difference between the House and Senate branches of Congress is the minimal eligibility requirements for election. In order to run for a seat in the House of Representatives, a candidate must be 25 years old, must have been a US citizen for at least 7 years and be a legal resident of the chosen state. To run for a Senate seat, however, a candidate must be 30 years old, and have been a US citizen for at least 9 years.

While the House of Representatives may reflect a wide spectrum of political views, from extremely liberal to extremely conservative, the Senate tends to be far less expansive. Members of Congress not only represent the wishes of their districts or states, but also their political parties' overall agenda. Members of the House of Representatives often form smaller factions based on similar political goals, gender, race or region of origin. Senators from the same state, however, may not even agree with each other politically. Support for bills pending in the Senate generally fall more reliably along political party lines than in the House of Representatives, where members may not feel as pressured to vote along party lines.

One noticeable difference between the Senate and House of Representatives is the amount of political clout. While House Representatives work hard to create laws and obtain government funding beneficial to their districts, they are not often viewed by their political parties as presidential material. Senators, on the other hand, have much more time to develop the sort of political support necessary to mount a presidential campaign. Therefore, a number of House Representatives will often run for open Senate seats in their states first, in order to position themselves for higher offices.