In the past 6 months, there has been increased interest in adding something analogous to C structs to the SIDL language and the Babel language interoperability tool. In particular, Rob Armstrong, of the Common Component Architecture, said the lack of structs 'is an oft-cited reason that people can't use Babel.' Because the interest is high and lack of structs is a barrier to Babel adoption, we must carefully consider the current work around, the motivations for structs, the implications of adding structs, and the alternatives for structs in SIDL/Babel. This document provides the background necessary for a discussion of structs in SIDL/Babel. For the purposes of this document, I am going to call the potential new language feature a SIDL struct.