"ALTERNATE HUSBANDRY", issued as Joint Publication No. 6 by four of the Imperial Agricultural Bureaux (Aberystwyth. 5s.), has been compiled by a number of authors, each of whom deals with different aspects of the subject. It is emphasized that the use of leys in rotation under a wide range of climatic and soil conditions and in combination with a great variety of crops is a question upon which much research is needed, and that the purpose of the publication is largely to provide a basis for that research. The system is flexible, but cannot be applied to all types of agriculture, it being unsuitable, for example, in semi-arid or wet tropical regions where problems of establishment and management multiply considerably. The publication opens with a geographical review in which the trends of development in the practice in fifteen different countries and regions are described. Later chapters deal with the question in more detail, showing among other matters that the type of ley selected depends largely on the climatic factor, and that a closer study of the root systems of herbage plants is required before the effect of the various species and their different combinations on the soil can be properly assessed. It is generally recognized that a ley is a method for improving the structure of the soil, as it increases granulation, which both benefits the crop and helps to prevent erosion. Other problems such as weed control, soil conservation, plant health and the economic factors involved in the system are also discussed. As regards the animal crop many factors are involved; but it seems likely that the regular ploughing of grassland will reduce the liability to disease even in spite of increased concentration of stock. For those requiring more detailed information, a list of more than three hundred references are arranged in groups appropriate to each chapter.