Scientific literature pertaining to the investigations on insect–plant interactions spans more than a century. This is a challenging frontier area today as it was for the pioneers, and it would continue to be so for researchers in their pursuit to help elucidate the complex relationship between the insects and plants. Despite the ready availability of exhaustive literature on this subject, the mechanisms of insect–plant interactions are still not completely understood. Insect–plant interaction is an extremely rich subject that transcends several disciplines of science and has far-reaching implications, especially in the management of ecosystem and crop protection. The interaction between pests and plants starts at the interface of plasma membrane and in response to perception of a pest and release of herbivore-associated molecular patterns (HAMPs); plants respond quickly by setting up the electrical signalling followed by depolarization of membrane, leading to increase in Ca²⁺ ion concentration and activation of calcium-sensing proteins. Further, this interaction is primarily governed by various signalling mechanisms, such as mitogen-activated kinase (MAP-kinase), jasmonic acid (JA), salicylic acid (SA) and ethylene (ET)-based pathways that regulate changes in gene and protein expression leading to synthesis of defensive compounds. Plants defend themselves not only by direct means but also by indirect means, wherein plants emit volatiles to attract natural enemies of the herbivores. Herein, we summarize the molecular and ecological aspects of complex insect–plant interactions to enable researchers to direct their course of action towards addressing them for making a meaningful contribution in this field, which will have far reaching implications in the success of insect pest management programs.