This chapter provides an overview of the Daisy model, with special focus on the model for plant uptake of water and nitrogen (N), and related processes. The loss of N from agriculture into aquifers and surface waters is recognized as a threat to surface and groundwater quality. Therefore, agroecological models capable of simulating the N dynamics in agricultural soils have been developed to support decisions and management related to N in agriculture. In Denmark, the problem of managing N in agricultural systems was recognized in the 1980s, and this prompted the development of the physically based Daisy model. The chapter proposes a model for simulating uptake of soil–water and N. The model is based on the single-root approach. A version where the root distribution is made a function of rooting depth and development stage is also included in the Daisy model as an option.