Recent studies suggest that climate change over the next century will affect water cycles all over the world, with precipitation decreases expected for many arid and semiarid regions. This will be particularly critical on hillslope areas under rainfed conditions, where only the amount of rainfall determines the success or failure of agriculture. Under these conditions, scarce and erratic rainfall produces runoff of an intermittent character, while infrequent rain of high intensity increases the soil erosion rate. It has therefore been suggested that agricultural production on hillslope areas combined with runoff water harvesting in arid and semiarid zones can be a viable solution to increase water availability to crop plants. In this water management system, water harvesting involves inducing, collecting, storing and conserving local surface runoff. This water can be used for supplemental irrigation of agricultural systems in rainfed areas, helping to maintain and even increase food production in these regions. This chapter analyses the potential of combining agricultural production with water harvesting in arid and semiarid zones through a comprehensive review of the literature on runoff water harvesting published during the past 25 years, which can be roughly divided into experimental and modelling approaches. The potential synergistic effects of water harvesting combined with agroforestry are illustrated by a practical case study using the results of a pilot experiment carried out in a semiarid region of Chile.© 2011 by Nova Science Publishers, Inc. All rights reserved.