Since the early days organic synthesis has remained an important branch of chemistry, but ecological chemistry has developed since the 1970s. It is a new and interdisciplinary branch of science with deals with biology and chemistry via interand intraspecific interactions among organism by means of organic compounds. On the other side, agents of crop protection have a long-known history. In the beginning, they were generally inorganic compounds, often non-selective, active only at high application rates, and frequently toxic. For example, the legendary Bordeaux mixture presented the first modest weapons to be applied in the battle against diseases of potatoes and vines. Aiming of finding less toxic, selective chemical active ingredients for crop protection applications, organized industrial research started 1930s, when DDT, 2,4-D, TMTD (Thiram) and Parathion (E 605) were discovered. During this period it has been established that chiral compounds are mostly active than non-chiral ones. Our knowledge in chemical ecology increased dramatically during the last two decades. Synthesis of stereoisomers of chemicals has clarified their structurebioactivity relationships to reveal the unprecedented diversity in the stereochemical aspects of crop protection agents. A selection of our data will be presented. The place and roles chemical ecology and stereo selective organic synthesis will be discussed.