Background: Sustainability reporting has become increasingly important for firms that want to appease their stakeholders and the society, whilst possibly increasing the corporate financial performance (CFP) of the firm. This is because sustainability disclosures currently work as the main channel for firms to inform their stakeholders of the CSR practices and environmental management carried out by the company. However, there have been various previous studies that examine the relation between corporate social performance (CSP) or the reported CSP, and CFP but not a study that would focus on GRI’s adherence level and its effect on Firm value (FV). The adherence level in the context of a GRI Report refers to the extent to which the GRI Sustainability Reporting Framework and GRI Standards have been applied to a company’s sustainability report (Global Reporting Initiative, n.d.). This study intends to examine if stakeholders can be affected by a sustainability report’s adherence ranking made by GRI, although there necessarily would not be a clear connection to a company’s actual environmental performance.  Purpose: The purpose of this study is to find out if the adherence level affects a firm’s value and how, although this classification of reports would not say anything about a company’s level of sustainability or a company’s sustainability performance. In short, the study wants to examine if stakeholders or the society surrounding a company are affected by the adherence level of a company’s GRI reporting and if this then can affect the value of the organization in any way. Aim: The aim of this research is to encourage organizations to become more transparent or elaborate regarding their sustainability practices if any significance between the adherence level and the FV can be found.  Method: This study was conducted by examining 98 European manufacturing firms’ GRI adherence levels for the years 2017 to 2019 and comparing them to respective Firm Values (Tobin’s Q) by the usage of panel data regression analysis.  Conclusion: The results show that no significant relationship between the GRI adherence level and FV can be found in the European manufacturing industry for the period 2017 to 2019.