Process-based growth models are rarely used as a basis for decisions in forest management. Reasons for this are discussed and the development and application of PROMOD, a simple process-based plantation productivity model designed to meet the needs of managers, is described. In particular,PROMOD is intended for screening prospective plantation sites on the basis of readily available input data, including site latitude, soil characteristics, and long-term climate data. Originally developed for use with Eucalyptus globulus Labill., PROMOD has since been parameterized also for Eucalyptus nitens (Deane & Maiden) Maiden and Pinus radiata D. Don. We discuss the adaptation of PROMOD to new environmental conditions and species; the sensitivity of the model's predictions to changes in model structure, the values of its physiological parameters and the accuracy and resolution of site survey information; and the use of the model both in assessing the profitability of plantation irrigation in semi-arid regions, and for generating broad-area productivity maps.