This study analyses how Spanish universities are communicating their commitment to sustainability to society. That entailed analysing the content of their websites and their scientific papers in sustainability science and technologies and measuring the impact of such research in social media. Results obtained from bibliometric approaches and institutional document analysis attest to intensified interest in sustainability among Spanish universities in recent years. The findings revealed an increase in the number of universities using terms associated with sustainability to designate the governing bodies. The present study also uses an activity index to identify universities that devote high effort to research on sustainability and seven Spanish universities were identified with output greater than 3% of the total. Mentions in social media were observed to have grown significantly in the last 10 years, with 38% of the sustainability papers receiving such attention, compared to 21% in 2010. Publications in open access journals have had a greater impact on social media, especially on Twitter and Facebook. The analysis of university websites showed that only 30% had social media accounts and only 6% blogs specifically designed to disseminate their sustainability activities.