The ability to predict net carbon exchange and production of vegetation in response to predicted atmospheric and climate change is critical to assessing the potential impacts of these changes. Mathematical models provide an important tool in the study of whole plant, canopy and ecosystem responses to global environmental change. Because this requires prediction beyond experience mechanistic rather than empirical models are needed. The uniformity and strong understanding of the photosynthetic process which is the primary point of response of plant production to global atmospheric change provides a basis for such an approach. Existing modelling systems have been developed primarily for expert modellers and have not been easily accessible to experimentalists, managers and students. Here we describe a modular modelling system operating within Windows to provide this access. WIMOVAC (Windows Intuitive Model of Vegetation response to Atmosphere and Climate Change) is designed to facilitate the modelling of various aspects of plant photosynthesis with particular emphasis on the effects of global climate change. WIMOVAC has been designed to run on IBM PC compatible computers running Microsoft Windows. The package allows the sophisticated control of the simulation processes for photosynthesis through a standardised Windows user interface and provides automatically formatted results as either tabulated data or as a range of customisable graphs. WIMOVAC has been written in Microsoft Visual Basic, to facilitate the rapid development of user friendly modules within the familiar Windows framework, whilst allowing a structured development. The highly interactive nature of controls adopted by WIMOVAC makes it suitable for research, management and educational purposes.