Identifying mechanistic patterns in seed development common across species would be extremely useful for understanding genetic and environmental limitations on seed development. The three classical stages of seed development (i) rapid gain in fresh weight associated with cell division and expansion, (ii) rapid cell enlargement to accommodate reserve deposition, and (iii) loss of fresh weight as the seed undergoes maturation drying, provide a useful framework for comparison. But the descriptive rather than mechanistic nature of these stages precludes assigning common developmental mechanisms across species. We have shown recently how seed water relations play a key role in controlling the rate and duration of grain-filling. These studies have exposed a number of developmental processes in common to wheat, maize, soybean and sorghum seeds. Relationships between seed water content and dry matter accumulation, in particular, are remarkably robust across species and environmental conditions. This poster will present the commonalities among wheat, maize, soybean and sorghum seeds as well as highlight specific differences within the same mechanistic framework. The use of this knowledge for advancing seed modeling and gene discovery will be discussed.