Companies of different size and sector regularly publish sustainability reports in order to record and disseminate their activities aimed at contributing to sustainable development and to refl ect their corporate social responsibility. From the various existing suggestions for such reports, the principles and guidelines of the Global Reporting Initiative are most widely used – at least among large companies. The very detailed guidelines and indicator system aim at supporting companies to provide relevant, balanced, comparable, accurate, timely, clear and reliable information on corporate activities and performance, while focusing on sustainability-context and stakeholder inclusiveness in their “non-financial” reporting. However, based on research into the content and quality of non-financial reporting, it is difficult to clearly conclude just how comparable and transparent the reports are, as well as to decide whether they truly refl ect the sustainability performance of the reporting companies. The paper provides a literature review and a qualitative analysis on the reporting practice of 37 large companies.