A physiologically based steady-state model of whole leaf photosynthesis (WHOLEPHOT) is detailed which describes the functional dependence of net photosynthesis in C 3 leaves on [CO 2 ], [O 2 ], incident radiant flux (PhAR), and leaf temperature. The model simulates among other phenomena a) observed [CO 2 ], [O 2 ], and temperature effects on the initial slope of light response curves, b) a C 3 type temperature response curve of net photosynthesis, c) a shift of the optimum temperature of net photosynthesis to higher temperatures with increasing light intensity, and d) observed temperature and [O 2 ] effects on the CO 2 compensation point. Model parameters are derived from published response data of several C 3 species. Simulations also demonstrate that parameter changes based on literature data result in acclimation-like changes in net photosynthesis response with respect to light intensity and temperature. The advantages of this model are that the number of parameters is minimized in order to focus on environmental effects and that all parameters can be determined from measured net photosynthesis responses.