Nondeterminacy occurs commonly in computing, much more than we recognise. Indeed it deserves to be recognised as a fundamental notion, meriting a place alongside other fundamental notions such as algorithm, recursion, data type, concurrency, object, etc. Essentially the same notion of nondeterminacy manifests itself in a range of different contexts, among them imperative, functional, and concurrent programming, competing agents, data refinement, and fixpoint theory. Nondeterminacy can be recognised, extracted, and studied in isolation such that the properties we discover are applicable more-or-less without change in the various domains in which it occurs.