||In recognition of the complexity of factors which affect the improvement of maize yields and productivity in different farming systems throughout the developing world, panels of crop research and extension experts assessed the relative importance of abiotic, biotic, crop management and socioeconomic constraints in a dozen major maize production systems in developing regions which are characterized by severe poverty, as indicated by child stunting. Maize plays an important role in household nutrition and poverty reduction in each of these farming systems. Drought has been identified as a major priority for maize improvement programs in international agricultural research, and especially in Africa and Asia. However, it is generally accepted that a variety of other “secondary” constraints limit maize productivity in good seasons, as well as in drought years. The well known CABI data base contains comprehensive but rather general information on losses and distribution. CIMMYT has conducted a number of studies with valuable information on constraints, and CIMMYT scientists have scored the severity of maize production constraints. However, few of these studies provide sufficient contextual information to extrapolate the results across zones, seasons and years. In these circumstances, this study organized the systematic tapping of the tacit knowledge of experienced research and development practitioners to provide valuable information on the relative importance of different production constraints and traits. The results of this study can be a checklist and guide to those involved in maize breeding and crop systems research and development by prioritizing key traits for the improvement in each of the systems.