It has been known for a long time that varieties of maize differ greatly in their response to different environments, Many varieties are specifically adapted to a very narrow range of climatic or edaphic factors, while others are adapted to a much wider range of environmenta1. factors. Unfortunately, little systematic information has been collected concerning this important aspect of maize breeding and production. As part of the CIMMYT Maize Program the International Maize Adaptation Nursery (IMAN) has been designed to test initially the adaptation of maize varieties from many areas of the world over a wide range of latitudes, climates, fertility conditions, water management and disease and insect complexes. Not only will these trials serve as a source of fundamental information concerning the adaptability of maize, but also they will provide a means of testing promising material on a much broader basis than is usually available to an individual breeder; and s.erve as a source of new, valuable genetic material for use by the cooperator either directly or in crosses. Because the first adaptation trials have been designed to assess the performance of maize varieties from widely different environmental and geographic situations, the performance of some of them is certain to be disappointing at particular test sites. However, the information gained from the trials will be invaluable as a guide to the breeders in their search for improved germplasm. The results of the International Maize Adaptation Nursery will be statistically analyzed and published for general distribution. It is important that cooperators study carefully the following pages which provide suggestions for the conduct of the nursery and the note-taking techniques. The value of these nurseries will depend to a large degree on the quality_ of the data which is returned for analysis. It is understood that any country collaborating in these tests will be free to use any of the material included in the nursery, either as parental material or as commercial varieties. In this latter case, the source (i.e. country) of origin of the variety or line under multiplication should be recognized.