Allelopathy refers to the beneficial or harmful effects of one plant on another, including both crop and weed species. Mushrooms is one such example which provides various effects to their curcumjacent plants by releasing allelochemicals. The authors’ of this book examine the allelopathy of mushrooms and showed that all mushrooms have allelopathic activity without exception. Furthermore, rice, barley, wheat, rye, sorghum and sunflower are known to be allelopathic crops. The authors focus on buckwheat in particular, to determine whether or not it is allelopathic as well. Other chapters examine the allelopathic effects of macrophytes in subtropical shallow lakes; and the invasive potential of parthenium weed, a herbaceous plant, and one that has now invaded over 44 countries worldwide, having an impact upon both crop and pasture production, natural community biodiversity and human and animal health.