Recovery of oxygen (O2) from water will be needed on future long-duration manned space missions. Direct electrolysis of cabin water vapor into O2 and hydrogen (H2) offers the advantage of avoiding the phase change, separation and handling of liquid water in zero gravity. These considerations affect liquid electrolysis subsystems which are presently baselined for central O2 generation aboard the Space Station. This paper presents the results of a technology development program that Life Systems, Inc., in cooperation with the National Aeronautics and Space Administration (NASA) Johnson Space Center (JSC) has been undertaking. The goal of the program is to develop Water Vapor Electrolysis (WVE) hardware that can selectively be used as localized topping capability in areas of high metabolic activity without oversizing the central Air Revitalization System (ARS). The electrochemically-based WVE interfaces with cabin air that is controlled in the following ranges: dry bulb temperature of 292 to 300 K (65 to 80 F); dew point temperature of 278 to 289 K (40 to 60 F); relative humidity of 25 to 75% and pressure of 101 ± 1.4 kPa (14.7 ±0.2 psia). The paper covers design requirements, construction details and presents test results of both single-cell and multi-cell module testing. Preliminary sizing of a multi-person subsystem will also be presented.