Kiwifruit growers in New Zealand are paid premiums for the dry matter proportion (DMP) of fruit, because fruit with higher DMP is generally preferred by consumers. In order to model the seasonal development of DMP in the fruit, and its response to environment and management, both the water and dry matter accumulation rates in the fruit need to be considered. Here we developed a biophysical model of kiwifruit berry development using the approach of Fishman and Genard (1998), in which accumulation rates of water and dry matter are driven by properties of the plant stem (stem water potential and the concentration of sugars in the phloem), and of the environment (temperature and humidity). Extensions to the original model are discussed, including the effects of adding an elastic component of growth, a pedicel, and a starch sub-model. The model describes fruit development throughout the growing season, including both the cell division and cell expansion phases. This extended modelling period requires that many parameters of the model change as the fruit develop. In kiwifruit, there is a marked change around 50 days after bloom, when the rate of water accumulation drops considerably, while dry matter accumulation continues relatively unabated. These changes increase the number of parameters required, making parameterisation difficult and a little ambiguous. Progress has been made towards measuring some parameters independently, but others have been either taken from the literature or simply chosen so that the overall behaviour of the model matches observations. Aspects of the model that require further research are identified