The purpose of this guide is to help agronomists identify, in a simple, stepwise fashion, maize production problems in the field. The guide may also contribute to improved consistency in agronomic observations and to identifying important questions for farmer interviews. Once problems are diagnosed, the lists of possible solutions may help in identifying factors to include in experiments. The information presented represents the collective knowledge of many experienced maize scientists. The diagnostic procedures found in this guide are not intended to replace experimentation but rather to help improve the efficiency of problem identification and the appropriateness of experiments designed to generate agronomic recommendations. Readers are encouraged to interpret and, when necessary, modify the diagnostic guidelines presented to match more closely their particular agronomic and environmental circumstances. Please feel free to send comments to CIMMYT headquarters on the guidelines and procedures.