A Sims 3 expansion pack code (often called a product code or serial code) is a unique 20-digit alphanumeric string used to verify that you own a legitimate copy of the game. Without this code, you cannot install the game or register it to your account.

Whether you are playing the old disc version or the modern digital version via Steam or the EA App, that code is the key to unlocking your content.

If you bought the Expansion Pack on Steam, the code is usually automatically applied. However, if you need to see the code (perhaps to register it on the EA App or the old Sims 3 website):

If you still have the CD/DVD case and the manual, you are in luck—but you have to know where to look.