This paper motivates the use of agent-based modelling to study policy impacts on systems of heterogeneous, individually acting agents, such as agricultural structures. The paper presents the model AgriPoliS and an application to a region in southwest Germany. The policies considered in the simulation experiments aim at increasing the efficient allocation of production factors. Results show that policies providing incentives for small farms to leave the sector speed up structural change and increase efficiency. The paper ends with an extensive discussion of model results, and the approach.