Data and their carriers work in tandem with each other. Data needs a carrier, whether it is a sheet of parchment, a glass negative plate or a PDF file. Clearly, if you work with digital information objects, you’ll need to find out as much as possible about the media that carry the information in question, i.e. file formats. The organisation curating the information needs to have a policy on file formats. That means deciding what guarantees it is willing and able to give about preservation, and how it should communicate about preservation issues with suppliers (and users) of the material. The Dutch Digital Heritage Network (NDE) is currently preparing an on-line tool for helping archives and heritage organisations to formulate a policy on file formats. This tool will be known as the Guide to Preferred Formats. It will consist of two parts, i.e. explanations and examples intended to help organisations in formulating a policy on preferred formats, plus a list of file formats with detailed information on each of them. The Guide to Preferred Formats will be overseen by an ‘expert group on preferred formats’. The expert group’s remit will be to bring together, share and refine the expertise currently available in the Netherlands.