The increasing global population and dwindling water supplies make efficient use of irrigation water the prime priority in agricultural production. The importance of irrigation water efficiency is more intensified now owing to concerns about climate change, which may lead to a drier climate in the future. Even though irrigation efficiency is a term widely used by plant physiologists, agronomists, irrigation engineers, and economists, both the definition and the perspectives of the term vary with the different disciplines. This review presents and compares irrigation water use efficiency from the perspective of different disciplines. This can help researchers in different fields understand each other's perspective and stimulate multidisciplinary thinking and research.