This paper aims to analyze sustainability practices in organizations. Specifically, the paper aims to: (i) develop a framework of key performance indicators for assessing and mapping sustainability practices of companies in a standardized form; (ii) explore which sustainability practices do companies report; (iii) explore the differences in sustainability practices between small and medium-sized enterprises and large organizations. Data for this study have been collected by means of secondary sources (i.e. companies’ websites and reports). Overall, 2,000 companies have been assessed based on the sustainability framework that has been developed, thus providing an unprecedented source of information for exploring and researching sustainability practices in organizations. Our results contribute to the debate on sustainability reporting and disclosure in different ways. The first methodological contribution consists in the development of a measurement framework that builds on existing sustainability frameworks designed mainly for large public organizations, but appropriately adapted to SMEs. The second contribution refers to the analysis of sustainability practices by comparing SMEs and LEs. To our knowledge, this is the first study that compares SMEs and LEs by using such a large amount of data, thus detailing whether “size matters” when it comes to embed sustainability into organizational processes