Inspired by challenges in designing energy technology policy in the face of climate change, we address the problem of decision making under “deep uncertainty.” We introduce an approach we call Robust Portfolio Decision Analysis, building on Belief Dominance as a prescriptive operationalization of a concept that has appeared in the literature under a number of names. The Belief Dominance concept synthesizes multiple conflicting sources of information to uncover alternatives that are intelligent responses in the presence of many beliefs. We use this concept to determine the set of non-dominated portfolios and to identify corresponding robust individual alternatives, thereby uncovering viable alternatives that may not be revealed otherwise. Our approach is particularly appropriate with multiple stakeholders, as it helps identify common ground while leaving flexibility for negotiation. We develop a proof-of-concept application aimed at informing decisions over investments into clean energy technology R&D portfolios in the context of climate change and illustrate how Robust Portfolio Decision Analysis helps identify robust individual investments.