The notion of control dependence underlies many program analysis and transformation techniques used in numerous applications. Despite wide application, existing definitions and approaches to calculating control dependence are difficult to apply seamlessly to modern program structures. Such programs structures make substantial use of exception processing and increasingly support reactive systems designed to run indefinitely. This paper revisits foundational issues surrounding control dependence and develops definitions and algorithms for computing control dependence that can be directly applied to modern program structures. In the context of slicing reactive systems, the paper proposes a notion of slicing correctness based on weak bisimulation and proves that the definition of control dependence generates slices that conform to this notion of correctness. Finally, a variety of properties show that the new definitions conservatively extend classic definitions. These new definition...