The seed systems of RTB (root, tuber, and banana) crops are unique because they are propagated from vegetative parts of the plant, not from true seed. RTB seed is thus bulkier, more perishable, and more subject to the attacks of pests and diseases than is true seed. Because of this, there is often a gap between potential and real crop yields, which seed interventions seek to narrow. Seed systems are formal or informal networks of people and organizations that produce, plant, and distribute seed. Informal systems may deliver low quality seed, but not always. This book describes 13 RTB seed system interventions, using a framework based on the concepts of seed availability, access, and quality. The 13 case studies included (1) a potato-growers association in Ecuador, (2) a hydroponic seed potato in Peru, (3) a yam seed technology in Nigeria, (4) a banana and plantain project in Ghana, (5) a sweetpotato seed project in Tanzania and (6) one in Rwanda, (7) a seed potato system in Kenya, (8) cassava in Nicaragua, (9) seed potato in Malawi, (10) disease-resistant cassava varieties in seven African countries, (11) a tissue culture banana project, (12) an emergency plantain and banana project in East Africa, and (13) a large cassava seed project in six African countries. Good seed may be available, but farmers may not have access to it if delivery channels are poor, if the seed is too expensive, or if farmers do not know about it. Without an intervention (e.g., a project), seed is produced on-farm; shared among friends, neighbors, and family; and sold in local markets (i.e., in an informal system). Some interventions try to organize farmers into new seed delivery channels. Some of these interventions succeed better than others. Seed can be distributed with vouchers, but that has a high administrative cost. Farmer organizations (or private companies) that are already well-structured may do a better job at distributing seed; but community nurseries can also be organized, especially if the goal is to distribute a new variety to farmers as a one-off, and not to create a permanent seed-supply enterprise. Most of the interventions in this book had some information on farmer demand, but not necessarily a rigorous understanding of the seed system. In spite of this, most of the new seed met farmer demand. Most interventions worked with improved varieties, but seed interventions could favor native varieties. Genetic purity is easier to manage in RTB crops, which breed true (they are clones), but seed health must be carefully managed. Market integration is important for developing a seed system. The seed can be made affordable by subsidies, for example, but farmers are more likely to buy seed if they can sell their harvests, or if they need a new variety to meet market demand (e.g., from a food manufacturer). The interventions described in this book did a fairly good job of linking stakeholders in mutually beneficial ways.