Many decisions must consider multiple, generally conflicting, decision objectives. And many decisions require not a single solution alternative, but a set or portfolio of alternatives. A business will generally produce a portfolio of products. Government will raise revenue through a portfolio of taxes. A prospective college student is wise to apply to a mix of schools, increasing the likelihood of at least one acceptance. A project team leader needs to select several team members, creating a balance of skills and taking into account the synergy of the team. While the single solution alternative decision problem has been widely studied and many solution approaches and decision support systems have been developed, the portfolio problem has been largely neglected. Specific problem environments have been discussed using heuristic, ad hoc methods, but no general methodology has been developed. This research focuses on identifying the characteristics of portfolio problem, on developing theoretical concepts and formal models to be used in identifying problem types in real world decision environments, and on mapping possible solution techniques to these models.