The relevance of simulation approaches to the study and design of agricultural production systems is widely claimed. The methodology and computer software appropriateto such a task have however still not reached the state of a mature technology and are mainly developed in research laboratories. Suitable computer models need to represent the structure and dynamics of the underlying biophysical system together with the coordinated human activities involved in the management of the farm production process. Most existingapproaches focus primarily on biophysical processes.This paper outlines the generic framework DIESE especially designed for building and running agricultural production system models. DIESE relies on a rich conceptual basis under the form of an ontology of agricultural production systems. It supports the modelling of the decision process in terms of activities, resources required to realize them, and well-structured constraints bearing on the relevance and feasibility of activities, the interdependencies between them and the restrictions on the uses of resources.Computationally the ontology comes under the form of a C++ library. In developing a farm production system model, the ontology acts as a metamodel; implementing a model amounts to particularizing the ontology concepts as required by the domain and then instantiating the corresponding classes to capture the specific aspects of the system to be simulated. A discrete event simulation mechanism realizes the step by step interpretation of the strategy and the progressive execution of the decided activities, which in turn alters the biophysical state that otherwise responds to external factors, e.g. weather, influencing biophysical processes.DIESE is currently used in large modelling projects dealing with various kinds of production such as cash crop, vineyard, pasture-based livestock and pig systems, which attest to the wide scope of applicability of the framework.