It's important to know that all of these steps must occur before a bill becomes law, but none of them are mandatory once the process begins. The process could end at any stage, at which point the bill is considered effectively dead.

In fact, this is what happens to most bills. Of the eight- to ten-thousand bills that are introduced during each General Assembly, only about 10% make it through all of the stages and become law.
 

The General Assembly, or the legislature, is made up of two chambers: the House of Representatives, commonly known as the House, and the Senate. The term "General Assembly" is also used to refer to the session in which the legislature is operating. Each session spans two years, starting in odd years. Each General Assembly is numbered sequentially, beginning when the legislature first met after Illinois became a state in 1818. Bills introduced at any point during a General Assembly are technically active during the entire General Assembly, although only very rarely are bills introduced in the first year but passed during the second year. Bills cannot, however, move between General Assemblies.

If a bill does not pass out of the legislature during one General Assembly, it must be re-introduced (and is assigned a new bill number) in order to start the process again in the new General Assembly. This is not generally an issue and bills are often introduced in numerous General Assemblies until they are finally passed.