The Software Sustainability Institute (SSI) was the first organisation in the world dedicated to improving software in research. It was founded in 2010 on the premise that helping individuals and institutions to understand the vital role that software plays in research would accelerate progress in every field of scientific and academic endeavour. The SSI set itself the ambitious goal of transforming academic culture by establishing the principle that reliable, reproducible, and reusable software is necessary across all research disciplines. Despite the magnitude of this challenge, the SSI has delivered substantive improvements and achieved a number of truly global successes. The case studies included in this report contain some of the highlights of the SSI’s 12-year history. These include playing a leading role in the creation and international adoption of an entirely new research role: the Research Software Engineer (RSE) (see CS2); creating a scalable and sustainable national training environment in which 7,000 researchers have improved their software skills (see CS8 and CS9); novel work on software citation that has been adopted by, amongst others, international research platforms and a leading multinational company (see CS6); and bringing about a shift in funding policy that benefits research in the UK and around the world (see CS5). Read our Midterm Review blog post for further background.