For the past thirty years, the need for ever greater supercomputer performance has driven the development of many computing technologies which have subsequently been exploited in the mass market. Delivering an exaflop (or a million million million calculations per second) by the end of this decade is the challenge that the supercomputing community worldwide has set itself. CRESTA brings together four of Europe’s leading supercomputing centres, with one of the world’s major equipment vendors, two of Europe’s leading programming tools providers and six application and problem owners to explore how the exaflop challenge can be met. CRESTA focuses on the use of six applications with exascale potential and uses them as co-design vehicles to develop: an integrated suite of technologies required to support the execution of applications at the exascale. The applications represented in CRESTA have been chosen as a representative sample from across the supercomputing domain including: biomolecular systems, fusion energy, the virtual physiological human, numerical weather prediction and engineering. Over the duration of the project, the aim is to deliver key, exploitable technologies that will allow the co-design applications to successfully execute on multi petaflop systems in preparation for the first exascale systems towards the end of this decade. At the heart of the proposal is the co-design process. The co-design vehicles are closely integrated to the systemware development, providing guidance and feedback to the systemware development work and to integrating and benefit from this development. A key feature of CRESTA is its use of dual pathways to exascale solutions. Many problems in HPC hardware and software have been solved over the years using an incremental approach. Most of today’s systems have been developed incrementally, growing larger and more powerful with each product release. However, we know that some issues at the exascale, particularly on the software side, will require a completely new, disruptive approach. CRESTA will therefore employ incremental and disruptive approaches to technical innovation – sometimes following both paths for a particular problem to compare and contrast the challenges associated with each approach.