A draft Act of Parliament is known as a bill.
In territories with a Westminster system, most bills that have any possibility of becoming law are introduced into parliament by the government. This will usually happen following the publication of a "white paper", setting out the issues and the way in which the proposed new law is intended to deal with them. A bill may also be introduced into parliament without formal government backing; this is known as a private member's bill.
In territories with a multicameral parliament, most bills may be first introduced in any chamber. However, certain types of legislation are required, either by constitutional convention or by law, to be introduced into a specific chamber. For example, bills imposing a tax, or involving public expenditure, are introduced into the House of Commons in the United Kingdom, Canada's House of Commons and Ireland's Dáil as a matter of law. Conversely, bills proposed by the Law Commission and consolidation bills traditionally start in the House of Lords.
Once introduced, a bill must go through a number of stages before it can become law. In theory, this allows the bill's provisions to be debated in detail, and for amendments to the original bill to also be introduced, debated, and agreed to.
In bicameral parliaments, a bill that has been approved by the chamber into which it was introduced then sends the bill to the other chamber. Broadly speaking, each chamber must separately agree to the same version of the bill. Finally, the approved bill receives assent; in most territories this is merely a formality, and is often a function exercised by the head of state.