If you already stored away your iMac box in the attic and neglected to jot down your serial number, there are two ways you can locate it. You will need your serial number if you ever have a need to call Apple for support and it is also required if you ever need to make a claim with your insurance company. If you are using Mac OS X, you can find your serial number in the About This Mac window. The other option is to look at the bottom of the foot of your iMac. This way can be a bit difficult especially if you have trouble reading small lettering.