The induction of resistance to disease during plant development is widespread in the plant kingdom. Resistance appears at different stages of host development, varies with plant age or tissue maturity, may be specific or broad-spectrum and is driven by diverse mechanisms, depending on plant-pathogen interactions. Studies of these forms of resistance may help us to evaluate more exhaustively the plethora of levels of regulation during development, the variability of the defense potential of developing hosts and may have practical applications, making it possible to reduce pesticide applications. Here, we review the various types of developmental resistance in plants and current knowledge of the molecular and cellular processes involved in their expression. We discuss the implications of these studies, which provide new knowledge from the molecular to the agrosystem level. Summary 405 I. Introduction 405 II. The many forms of developmental resistance 406 III. Molecular mechanisms of developmental resistance 410 IV. Relationships between defense and development in plants 412 V. Concluding remarks 413 Acknowledgements 413 References 413