Controlled environment chambers can be powerful tools for crop physiological research, as well as for predicting responses in the field, but this latter approach must be used cautiously.  If the final application is a controlled environment (CE) itself, then clearly CE research is appropriate.  This is the case for growing crops in space, where the crops could be used to generate O₂, remove CO₂, provide food, and purify water.  Obviously, space presents unique challenges, including reduced gravity (m-g for Earth orbit and transit, 1/6 g for the Moon, 1/3 g for Mars), high energy radiation, and various combinations of gases and total pressure.  In addition, if electric lighting is used, then spectral composition must be considered.  The tight atmospheric closure of space systems can also allow CO₂ and trace organic compounds to build accumulate.  For the past 25 years NASA has sponsored CE research with crops based on the vision that bioregenerative life support systems will eventually be needed for space travel.  This has generated interesting observations, including the ability to produce remarkable biomass yields, the ability to grow a wide range of crops in recirculating hydroponics, careful characterization of canopy gas exchange, including ethylene, and documenting peculiar responses such as elevated stomatal conductance at super-elevated CO₂ concentrations.  The final decisions for which life support technologies to use on a given mission will be based largely on economics, which provides impetus for cutting the costs and maximizing productivity.  This in turn could provide benefits on Earth as well as for space.