I would like to enter the name of an external file into a Excel cell so that I can use that name in excel formulas to refer to other spreadsheets.
Any ideas please?

Welcome to the Board!

Take a look at the INDIRECT() function, which will require the workbooks to be open. If you need to work with them closed, you can use INDIRECT.EXT, which can be found in the MOREFUNC add-in, which you can find here: http://longre.free.fr/english/index.html.

i.e. =INDIRECT("'["&C1&"]Sheet1'!$A$1"), where C1 holds the filename.

Hope that helps,

Smitty