Book excerpt: Biological and physiological systems: animal sciences. Plant-animal interactions in northern temperate sown grasslands and semi-natural vegetation. Exploitation of the systems approach in technical design of agricultural enterprises. Application of systems theory to farm planning and control: modelling resource allocation. Optimising the mixture of enterprises in a farming system. Farming systems research-extension. Food policy and food security planning: institutional approaches to modelling grain markets and food security in Sub-Saharn Africa. A systems view of commercial supply and marketing links. Agroecosystems. Understanding and managing changes in agriculture. Agricultural sector modelling for policy development. Of agricultural systems and systems agriculture: systems methodologies in agricultural education. Extension education: Top(s) Down, Bottom(s) Up and Other Things.