Complex socioeconomic linkages and interdependencies within and between nations have made planning and policy determinations for agricultural development increasingly difficult. To help solve agricultural sector development problems, computerized models using a broad systems perspective and simulation techniques are required. This four-part report, written for agricultural decisionmakers, policy analysts, and students of systems approach and economic development, explains a simulation approach for policy decisionmaking in agriculture. An introductory section presents a conceptual model of system simulation in which agricultural decisionmaking is approached from both an investigative side (acquisition, analysis, and synthesis of information) and an administrative side (decision, execution, and responsibility for action). Also presented in this section are discussions of the interaction of agriculture and the national economy, the theory and practice of model-building, the institutionalization of investigative capacity for decisionmakers, and the training of system simulation teams. The second section addresses the institutionalization of this model within the Ministry of Agriculture and Fisheries in the Republic of Korea, where the original model was developed. A presentation of the physical characteristics, socioeconomic structure, and institutional setting of the Korean agricultural sector is followed by an overview of the values held by Korean decisionmakers, problems encountered, design of the agricultural sector model, and policy areas which the model addressed. Korean population, national economy, technology change, resource allocation, trade, data requirement, and water development projections are also components of the model. Although dependent on the skills of analysts in selecting and linking components and explaining projected responses correctly, the model is seen as a powerful analytical tool. The third part consists of two Korean sub-sector models for a grain management program and for a government analysis of food grain pricing. Finally, future directions for the model, including its transferability and the development potential of the simulation approach, are discussed. A total of 52 illustrations, 34 tables, and 185 references (1947-77) are included.