Fertilizer use efficiency is important because careless application can lead to nutrient imbalances in the growth medium and excessive leaching of nutrients leads to environmental pollution. In the past, fertilizer recommendations for high value crops have rarely been influenced by economic considerations. The wide use of soilless media in greenhouse vegetable production now provides the opportunity for better nutritional control but routine fertilizer use has become an environmental concern. The ideal of optimal fertilizer application to a crop throughout the entire cropping season in accordance with the changing needs of the plants for nutrients has come close to reality in greenhouse tomato culture thanks to a greatly improved understanding of tomato nutrition and the availability of sophisticated fertilizer delivery systems. Although there is still a lot to learn, the general principles of crop response to the osmotic effects of the nutrient solution las measured by electrical conductivity, EC) and to the concentrations of most nutrients (e.g. N, P, K, Ca, Mg, and Fe) as a function of plant age and season are probably known best for tomato than any other horticultural crop; this makes the greenhouse tomato a preferred model crop in the development and testing of seasonal fertigation programs. With the advent of the computerized fertigator, the timely application, and evaluation, of a series of seasonal fertigation programs has now become practical and the objective of developing advanced seasonal fertigation programs attenable.