The Interaction Design Process
Problems are complex beasts. It is not enough to understand what you want to achieve, you also need to understand the context the problem exists in.
That context is made up of a number of aspects. The people who will use or interact with a system; the business goals; the technical capabilities and constraints and even the legal framework which the product will inhabit.
This was presented at the “Usability: What's the Use?” event at the CUBE in Manchester, Jan 28th, 2009.