  The Flexible Image Transport System (FITS) standard has been a great boon to
astronomy, allowing observatories, scientists and the public to exchange
astronomical information easily. The FITS standard, however, is showing its
age. Developed in the late 1970s, the FITS authors made a number of
implementation choices that, while common at the time, are now seen to limit
its utility with modern data. The authors of the FITS standard could not
anticipate the challenges which we are facing today in astronomical computing.
Difficulties we now face include, but are not limited to, addressing the need
to handle an expanded range of specialized data product types (data models),
being more conducive to the networked exchange and storage of data, handling
very large datasets, and capturing significantly more complex metadata and data
relationships.
  There are members of the community today who find some or all of these
limitations unworkable, and have decided to move ahead with storing data in
other formats. If this fragmentation continues, we risk abandoning the
advantages of broad interoperability, and ready archivability, that the FITS
format provides for astronomy. In this paper we detail some selected important
problems which exist within the FITS standard today. These problems may provide
insight into deeper underlying issues which reside in the format and we provide
a discussion of some lessons learned. It is not our intention here to prescribe
specific remedies to these issues; rather, it is to call attention of the FITS
and greater astronomical computing communities to these problems in the hope
that it will spur action to address them.
