Practical reasoning is reasoning about what is to be done. A decision on what to do may involve weighing the options open to an individual, taking into account dependencies on the actions of others, or complex collaborative decision-making. The role of argument in practical reasoning is explored in this chapter, both from a philosophical and computational perspective. In doing so, we discuss the use of computational systems in assisting people engaged in decision making, and, in particular, we investigate practical reasoning as joint deliberation between the human and decision support system. Such a system, it is argued, facilitates research into the use of argumentation techniques in computational models of practical reasoning, and the use of computational models to evaluate theories of practical reasoning.