Information architecture (also known as IA) is the foundation for great Web design. It is the blueprint of the site upon which all other aspects are built - form, function, metaphor, navigation and interface, interaction, and visual design. Initiating the IA process is the first thing you should do when designing a site.
Clients sometimes view the development of an IA to be impractical, both in terms of the time it takes and the skill needed to do it effectively. But this mentality is slowly changing. A good IA is incredibly effective, and knowing the basics of the IA process can save both time and money in the long run.