Emission of isoprene from vegetation affects tropospheric chemistry at the regional and global scales. Projected global climate change will potentially alter emission rates, with corresponding influences on concentrations of ozone and other radiatively important trace gases. Progress has been made in surveying plant species for their baseline emission rates and in understanding the physiology of the response of emission to environmental factors such as temperature, light and atmospheric CO2 concentration. However, few tree species of tropical environments have been studied nor have the details of isoprene biosynthesis or its functional significance been elucidated. Relatively simple emission models at regional to global scales have been developed using geographic databases for temperature and vegetation characteristics. Isoprene emissions are expected to rise in response to projected global climate change because of increases in temperature and an increased areal extent of high isoprene emitting forest types. There remains great uncertainty about such projections however, considering the uncertainties in the emissions modeling (about a factor of 3), uncertainties in the climate modeling, the future influence of anthropogenic factors on vegetation change, and the unmodeled influence of high CO2 on isoprene biosynthesis. There is a need to improve the modeling of emissions as inputs to global atmospheric chemistry models which in turn can be used to evaluate the effects of changing emissions on concentrations of tropospheric ozone and other radiatively important gases.