Add-ins are a useful feature in Excel, considered by many Excel developers to be an indispensable tool when distributing their custom projects to a wider audience. Anyone can create an add-in — it's the kind of thing that's easy to do once you know how. This lesson discusses the concept of add-ins and how to incorporate them into your Excel projects.
This lesson discusses standard Excel add-ins. Two other types of add-ins exist that are not developed with VBA and are not discussed in this lesson. One of the other types is called
COM add-ins, developed with languages such as Visual Basic, C++, and J++ that support Component Object Model components. The other type is
DLL add-ins, which are Windows files known as Dynamic Link Library files.
An Excel add-in is a special type of Excel workbook that has been converted to an add-in file. There is no magic to the add-in conversion process, but after you create an add-in file, you'll notice its unique characteristics:
The file extension is
.xla for Excel versions prior to 2007, and
.xlam for Excel versions 2007 and 2010.
Add-ins are always hidden; you do not open and view them as you would an Excel workbook.
You cannot show sheets of any kind belonging to the add-in file.
The add-in file is not recognized as an open workbook in the