The Transparency International (TI) Corruption Perceptions Index is a key instrument used to overcome difficulties in measuring corruption at a comparative level. The main aim of the present research is to assess the limits of this instrument and the implications that such limits have on our understanding of corruption in various forms. First, the challenges confronted in defining corruption in a precise framework hamper the measure and the conclusions that emerge from studies that use the index. Second, this conceptual problem is further amplified by the use of perceptions that are at the heart of the index. Although the TI Index is indispensable in accounting for corruptive practices and that its limits emerge principally when precautions are not taken in its use, the key challenge for users of this measure nevertheless remains the detection of corruptive practices in less transparent contexts that are not captured within the index’s current design.