"Capstone" is a metaphor used to describe a final achievement that builds upon previous works and encapsulates them. Capstone projects are included in engineering curricula to integrate multi-disciplinary subjects and teach professional skills that are difficult to impart in a traditional lectured course. Since these projects serve to transition students into professional engineers, they have a direct impact on a university's industry reputation and ranking. Therefore, it is worthwhile to study the capstone programmes implemented at the world's top-ranked engineering universities to discover common elements which characterise them. In this paper, common elements of the capstone programmes implemented in mechanical and aerospace engineering undergraduate programmes in the world's top-ranked engineering universities are identified and analysed to determine established best practices. These practices can be modelled and applied to the pedagogy of engineering programmes at universities around the world to improve the development of professional skills of future graduates. (Contains 2 tables and 1 note.)