Computer Science is deeply concerned with how computers and computer systems work, and how they are designed and programmed. Pupils studying computing gain insight into computational systems of all kinds, whether or not they include computers. Computational thinking influences fields such as biology, chemistry, linguistics, psychology, economics and statistics. It allows us to solve problems, design systems and understand the power and limits of human and machine intelligence. It is a skill that empowers, and that all pupils should be aware of and have some competence in. Furthermore, pupils who can think computationally are better able to conceptualise and understand computer-based technology, and so are better equipped to function in modern society. Computer Science is a practical subject, where invention and resourcefulness are encouraged. Pupils are expected to apply the academic principles they have learned to the understanding of real-world systems, and to the creation of purposeful artefacts. This combination of principles, practice, and invention makes it an extraordinarily useful and an intensely creative subject, suffused with excitement, both visceral (“it works!”) and intellectual (“that is so beautiful”). Computer Science and Information Technology are complementary subjects. Computer Science teaches a pupil how to be an effective author of computational tools (i.e. software), while IT teaches how to be a thoughtful user of those tools. This neat juxtaposition is only part of the truth, because it focuses too narrowly on computers as a technology, and computing is much broader than that. As Dijkstra famously remarked, “Computer Science is no more about computers than astronomy is about telescopes”. More specifically: