Controlled environments provide unique opportunities to study plant growth and development. Since photosynthesis drives almost all dry matter accumulation of plants, photosynthesis measurements can be a valuable tool in understanding how environmental or genetic factors affect plant growth. However, leaf photosynthesis measurements commonly are poorly correlated with plant growth. Canopy or whole-plant photosynthesis and respiration measurements, on the other hand, can provide accurate measurements of growth. This presentation will focus on different approaches to measuring canopy photosynthesis, ways to assure that the data are accurate, and interpretation of the data. Canopy photosynthesis measurements can be used not only to quantify the effects of environmental or genetic factors on plant growth, but also to determine some of the physiological reasons for such differences in growth. Among the physiological parameters that can be estimated from canopy photosynthesis measurements are carbon use efficiency, canopy quantum yield, and growth and maintenance respiration.