The concept of "substantial differences" - far from being a dry, technical topic for a book on higher education policy - goes to the heart of how we view qualifications and education and is the key concept of the Council of Europe/UNESCO Convention on the Recognition of Qualifications concerning Higher Education in the European Region, better known as the Lisbon Recognition Convention. What do learners know and understand and what are they able to do on the basis of their qualifications? How can this be expressed and described, and how can learners carry their qualifications across borders without leaving part of their real value behind?In discussions on substantial differences, the technical meets the philosophical, the administrative meets the political. Decisions on recognition, made in considering whether a difference is substantial, have a direct influence on applicants' future study and employment opportunities, but also reveal how those who make the decisions view themselves, their education system and their societies.