This book represents the authors' lifetime dedication to the study of inhibitors and phytohormones as well as its practical applications for achieving a more sustainable agriculture. Their work focuses on the functions of various groups of active molecules, their direct effect upon plant growth, but also implications for their impact upon the surrounding environment are explored. The main idea of the book evolved from the need to determine a balance among natural growth inhibitors and phytohormones. This approach was pursued through a better understanding of their biochemical pathways, their effects on plants physiological functions, and their influence upon stress factors on plant ontogenesis.