This chapter discusses recent advances in the use of agent technology in Decision Support Systems (DSSs) and introduces a model for an agent-based DSS. The chapter analyzes the modern requirements for the nature of decision support and argues in favor of adopting active situated paradigm as the basis for building DSS. The benefits of agent technology are highlighted in relation to the desired features of DSS and the past research in this direction is reviewed and systematically categorized. The description of an agent-based DSS elaborating on the architecture of the system and the potential use of data mining techniques is then introduced. The approach is illustrated with an agent-based DSS for investment decisions. The chapter informs the readers about the state of art in agent-based DSS, and provides a framework that can be used as a reference model in future research in the area.