Mechanical sowing refers to the placement of seeds into the soil by an agricultural machine or manually operated (but mechanical) device. Mechanical sowing, also referred to as mechanical seeding, is generally practiced in areas where there are constraints to labor availability or where farmers want to reduce the drudgery of planting seed by hand. It is typically utilized for cereal crops, but can also be applied to legumes and many other crops, including rice. When farmers or agricultural machinery service providers – people who own seeding machinery and rent out its use on an affordable fee-for-service basis – practice such seeding, the geometry of crop placement tends to be precise, so long as the machine is well calibrated, and correctly used and maintained (topics that are covered in this learning module). While mechanical seeding may not always result in increased yields, it does tend to save labor costs for farmers, and thus profit increases where yields are maintained compared to hand-sown seed. Further savings may result when farmers use mechanical seeding equipment that tills or prepares the soil at the same time as it sows seed, or where tillage is foregone, as in zero-till and conservation agriculture systems. Where the sowing date is critically important – for example, for wheat or maize grown in the tropics and sub-tropics – mechanical seeding can advance sowing dates, leading to potential yield increases compared to more time-consuming conventional planting involving multiple tillage passes and hand sowing. This book focuses on seeding machinery that can be attached to a two-wheeled tractor (sometimes called a ‘power tiller-operated seeder’, or PTOS), which typically has a rotovator to till the soil, and seed and fertilizer boxes with mechanisms to meter and place the seed and fertilizer into the soil in rows as the tractor moves forward. Other configurations exist, but we focus on the above because it tends to be the most commonly and commercially available seeding machine in South Asia, Southeast Asia and parts of Africa. More specifically, our focus is on two-wheeled ‘hand’ tractors (sometimes also called single-axle tractors) because of their wide suitability for smallholder farming conditions in both Asia and Africa, although they are also found in parts of Central and South America. The ‘scale-appropriate’ nature of this equipment for resource-constrained smallholder farmers is particularly appealing for agricultural development projects concerned with advancing appropriate technologies.