Screening is a process for multiple criteria decision analysis (MCDA) that reduces a large set of alternatives to a smaller set that most likely contains the best choice. To study screening in detail, MCDA is first interpreted as consequence-based preference aggregation. Consequence data and preference expressions (values and weights) are defined and the aggregation steps are elaborated. Based on these concepts, screening and sequential screening are defined and their properties are discussed. Then, it is shown how several popular MCDA methods can be integrated into a decision support system for sequential screening based upon available decision information. Finally, an illustrative application to water supply planning is presented.