'Plant Constituents and their Mechanism of Action as Pesticide' is a reference book specially prepared for researchers, teachers & professionals working on Natural Products. The book contains seven chapters; the experimental part includes the extraction, separation and identification techniques of the plant constituents, and detailed in vitro, in vivo and in silco investigations against agricultural pests. The in vitro studies against fungal pests, includes MIC, IC50, MKT, ID, pesticidal spectrum, synthetic comparison, using NCCLS, 2002 protocols with slight modifications. However, in vitro studies against insect pests, includes repellent toxicity, contact toxicity and fumigant toxicity. Further, how the findings of in vitro investigations can be useful for data prediction, using ANN modelling; ligand- protein interactions, using in silico (Online software used: CLUSTALW2, ESyPred3D and Phyre; off-line software used: Molegro Virtual Docker 3.2.0); and their validation in wet lab, using molecular techniques are arranged chronologically. Moreover, investigations in absence of reference protein for plant constituents can be a model for the scientist working on natural pesticide.