An add-in is supplemental functionality that adds custom commands and specialized features to Microsoft Excel. There are two types of add-ins, Excel add-ins and COM add-ins.
Here is how you can find out which add-ins are loaded.

Excel 2003:
- Excel add-ins are available at Tools > Add-ins.
- COM add-ins list is not available by default. Please see how to get to this list at Knowledge base article http://www.sigmazone.com/support/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=7

Excel 2007:
Go to Office button > Excel Options > Add ins. At the bottom of the dialog you will see 'Manage…' combo box.
- Select Excel add-ins and click 'Go…' to get to the list of Excel add-ins.
- Select COM add-ins and click 'Go…' to get to the list of COM add-ins.

Loaded add-ins are one that are checked.