Book excerpt: ILCA's policy towards modelling in the framework of livestock systems research; models and the analysis of productivity in extensive livestock systems in Israel; prediction of actual primary production under nitrogen limitation; behavioural aspects of intake at pasture in ruminats; prediction of feed intake in ruminats; relationships between chemical composition and voluntary intake of feeds by sheep and cattle; the effect of breeding season duration on production and feed consumption in grazing beef cattle in the south of Israel; adaptation of the Kahan model for a mixed farming system in southeastern Asia; appraisal of the ILCA cattle herd dynamics model using data from pastoral systems in mali and kenya; moddeling pastoral livestock production: problems and prospect; analysis of management impact in semi-arid agropastoral systems; modelling economic outcomes of livestock production systems; selection of sheep husbandy techologies under single and multiple goal constraints; types, purposes and users of models; problems related do intake.