A generic engineering trade study methodology has been developed to provide an effective framework for the system analysis of regenerative live support systems. The performance of engineering tradeoffs is a key technique in a rigorous system engineering process that is being used to develop advanced regenerative life support technology at NASA Ames Research Center. The trade study methodology consists of the following steps: 1) deriving relevant life support system functional requirements from a given space exploration mission scenario of interest; 2) developing a tradeoff decision methodology consisting of a set of evaluation criteria and corresponding weighting functions grouped into a relational hierarchy; 3) synthesizing a set of design options to be evaluated during the study; 4) modeling and analyzing each design option to generate data to input to a quantitative scoring scheme; and 5) evaluating each design option using the information developed in the preceding steps. These steps are repeated as necessary to optimize the design using an iterative cycle.This paper describes the trade study methodology in detail, using examples relevant to life support technology. The use of decision analysis techniques in the trade study method is emphasized. The role of a robust suite of mathematical modeling and analysis tools is described. Finally, expected enhancements to the methodology are outlined.