In a workshop sponsored by the Natural Resources Group (NRG) of the International Maize and Wheat Improvement Center (CIMMYT), scientists from the USA, Canada, South Africa and CIMMYT gathered at CIMMYT headquarters during 19-22 April, 1999, to examine the performance of leading maize and wheat simulation models, particularly CERES, for tropical environments of high and low yield potentials. Major outcomes are reported in this publication and include: * revision of temperature effects on development in CERES Wheat 3.5; * examination of strategies for modeling barrenness and prolificacy in maize; * identification of the temperature effect on radiation use efficiency as a priority for subsequent revision; * heightened recognition of the need to compile quality data sets for maize and wheat growth from diverse environments70 pages