The principle of proportionality looms very large in the law of armed conflict as it works as the compromising formula which balances the two competing interests; namely, humanity and military necessity. This has become a conventional rule after the Geneva Conventions, while it has also been identified as a customary international law principles for years. Though the principle plays a vital role in IHL in reducing the calamities of warfare, there is another side to the same issue because that has been vividly criticized. In this context, the objective of this article is to identify the conceptual and conventional foundation of the principle of proportionality and its pratical application, specially relating to the means and methods of warfare, terrorism and the protection of environment in times of warfare. It will also address the contemporary challenges and existing gaps and conclude with possible suggestions.