Reading matrices from Excel, CSV or formatted flat files

Hello!

I want to analyse large Input-Output matrices (Leontief matrices)
using Maxima.

I want to store them in some commonly readable file, like Microsoft
Excel file, or CSV file, or just a formatted text file. Then, I want
to load the data, contained in these files, into Maxima.

Is it possible to read data in Maxima from one of the data formats
mentioned above?

If not, what format is used normally for storing external data in
Maxima?

TIA

dap