What is a decision problem?

This paper presents a general framework about what is a decision problem. Our motivation is related to the fact that decision analysis and operational research are structured (as disciplines) around classes of methods, while instead we should first characterise the decision problems our clients present us. For this purpose we introduce a new framework, independent from any existing method, based upon primitives provided by (or elicited from) the client. We show that the number of archetypal decision problems are finite and so the archetypal decision support methods.