The Loess Plateau of China is unique in the world. For a long time many measures have been taken to improve the living condition and income of local farmers, agroforestry is one of the efficient ways. There are some intercropping models in the area, it is urgent to probe into the interaction among different species from the eco-informatics point of view to optimize the models. Therefore, allelopathic effects existing among intercropping species of the agroforestry systems practiced by local farmers in the loess area of northern Wei River of China, especially those of Juglans regia, Eucommia ulmoides, Acer trancatum, Prunus salicina on some crops and Chinese medicinal herbs, are revealed in the book. The releasing routines and the impacts of allelochemicals on germination and growth of seedlings of the crops and herbs, the characteristics of soil and rhizosphere, the effect mechanism, etc. are analyzed. The data collected, the intercropping models optimized and the management techniques suggested are valuable references for those who are interested in research and practice of agroforestry and allelopathy.