Overheard at the Reference Desk…What is the difference between a public law and the code?

Once a bill becomes a law, it is given a public law (P.L.) number indicating the congressional session and sequence number of its enactment. The first law of the 110th Congress is P.L. 110-1. These public laws are published in the Statutes At Large, the official publication for federal session laws.
But having to look up a law by the date of its enactment would be grueling research even for a law librarian, so fortunately the chronological public laws get codified. The U.S. Code is an arrangement of all the laws by subject called titles. There are 50 of them and they are divided into chapters and sections.