Among several technologies known for reducing carbon dioxide (CO2), the Sabatier and Bosch processes are the two primary options being considered for application in a regenerable Environmental Control and Life Support System (ECLSS) aboard the projected Space Station. Both processes reduce CO2 by catalytic reaction with hydrogen (H2) and enable the recovery of the metabolically consumed oxygen (O2). The Bosch process produces carbon and water while the Sabatier process produces methane and water. While the technologies involved with these processes are different, each must interface with similar subsystems of a regenerable ECLSS. This paper presents a comparison between the two competing technologies and includes the design and sizing of the respective reactors and other subsystem components for the Space Station application. The analysis includes comparison of process characteristics and identification of assumptions and ground rules, with particular attention given to defining subsystem boundaries. For a given technique, all the hardware required to reduce CO2 to a specified level fall within these boundaries. The analysis determines total equivalent weight, which includes fixed hardware weight and weight penalties for power and heat rejection requirements. Data for the subsystems were acquired through NASA and other published sources. This paper also examines the various merits of the Bosch and Sabatier CO2 reduction subsystems, including the advantages and disadvantages and operational impacts of both.