Don't worry. Not everyone knows it...

As we all know, C# doesn't support optional parameters(till framework 3.5) whereas VB does.In the same way, COM components don't support parameter overloading , so for each value in a parameter list, we've got to pass in something, even if it does nothing. Moreover, COM parameters are always passes by reference , which means we can't pass NULL as a value. In VB 2005, this is not really as issue because it supports optional parameters and we can just leave them out. But C# doesn't support this, so one have to create object variables and pass them in. See following code sample: u sing Microsoft.Office.Core; u sing Microsoft.Office.Interop.Excel;  // Must have office installed Application NewExcelApp = new Application; NewExcelApp.Worksheets.Add();       // This will not compile So, as a workaround, the Type.Missing field can be used and this field can be passed in with the C# code and the application will work as expected.  Check it in below code...