A proposal usually takes one of four principal forms: the bill, the joint resolution, the concurrent resolution, and the simple resolution.
Bills are laws in the making. A House-originated bill begins with the letters "H.R." for "House of Representatives", followed by a number kept as it progresses. It is presented to the president after both Houses agree.
Joint resolutions - There is little practical difference between a bill and a joint resolution since both are treated similarly; a joint resolution originating from the House, for example, begins "H.J.Res." followed by its number.
Concurrent resolutions affect only the House and Senate, and accordingly aren't presented to the president for approval later. In the House, it begins with "H.Con.Res."
Simple resolutions concern only the House or only the Senate and begin with "H.Res." or "S.Res." respectively
Most legislative proposals are introduced as bills, but some are introduced as joint resolutions. There is little practical difference between the two, except that joint resolutions may include preambles but bills may not. Joint resolutions are the normal method used to propose a constitutional amendment or to declare war. On the other hand, concurrent resolutions (passed by both houses) and simple resolutions (passed by only one house) do not have the force of law. Instead, they serve to express the opinion of Congress, or to regulate procedure.