Information and communication technologies (ICTs) have always mattered in agriculture. Ever since people have grown crops, raised livestock, and caught fish, they have sought information from one another. What is the most effective planting strategy on steep slopes? Where can I buy the improved seed or feed this year? How can I acquire a land title? Who is paying the highest price at the market? How can I participate in the government's credit program? Producers rarely find it easy to obtain answers to such questions, even if similar ones arise season after season. Farmers in a village may have planted the "same" crop for centuries, but over time, weather patterns and soil conditions change and epidemics of pests and diseases come and go. Updated information allows the farmers to cope with and even benefit from these changes. Providing such knowledge can be challenging, however, because the highly localized nature of agriculture means that information must be tailored specifically to distinct conditions. ICT has unleashed incredible potential to improve agriculture, and has found a foothold even in poor smallholder farms and in their activities. The ability of ICTs to bring refreshed momentum to agriculture appears even more compelling in light of rising investments in agricultural research, the private sector's strong interest in the development and spread of ICTs, and the upsurge of organizations committed to the agricultural development agenda. Each module in the Sourcebook discusses the key challenges, enablers, and lessons related to using ICTs in a specific subsector of agriculture. These are derived from a range of experiences, and summarize the knowledge gained during pilot projects and wider initiatives. While different in type of intervention and approach, a string of themes emerges from the modules: the why and how of using ICT in agricultural development.