Article I of the Constitution establishes the legislative or law making branch of government with the formation of a bicameral Congress. This system provides checks and balances within the legislative branch.
Only after much debate did the Founding Fathers agree on the creation of the House of Representatives and the Senate. A major issue was how representation in the legislative body would be determined. Delegates to the Constitutional Convention from larger and more populated states argued for the Virginia Plan that called for congressional representation should be based on a state's population. Fearing domination, delegates from smaller states were just as adamant for equal representation and supported the New Jersey Plan. Roger Sherman, a delegate from Connecticut, proposed the bicameral legislature. The Great Compromise, among other provisions, resulted in the creation of two houses, with representation based on population in one and with equal representation in the other.
Members of Congress are now elected by a direct vote of the people of the state they represent. It has not always been this way for the Senate. Prior to 1913 and the 17th Amendment to the Constitution, Senators were chosen by their state legislatures because the Senate was viewed as representative of state governments, not of the people. It was the responsibility of Senators to ensure that their state was treated equally in legislation.
Agencies that provide support services for the Congress are also part of the legislative branch. These include the Government Printing Office (GPO), the Library of Congress (LC), the Congressional Budget Office (CBO), the Government Accountability Office (GAO), and the Architect of the Capitol.